Polytrimethylene terephthalate resin

ABSTRACT

A polytrimethylene terephthalate resin comprising: 90 to 100 mole % of trimethylene terephthalate recurring units, and 0 to 10 mole % of at least one monomer unit obtained from a comonomer other than the monomers used for forming the recurring units and copolymerizable with at least one of the monomers used for forming the recurring units, which resin has the following characteristics: (A) an intrinsic viscosity [η] of from 0.8 to 4.0 dl/g; (B) an Mw/Mn of from 2.0 to 2.7; (C) a psychometric lightness L-value (L-1) of from 70 to 100 and a psychometric chroma b*-value (b*-1) of from −5 to 25; and (D) a psychometric lightness L-value (L-2) of from 70 to 100 and a psychometric chroma b*-value (b*-2) of from −5 to 25 as measured after heating the resin at 180° C. for 24 hours in air.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to JapaneseApplication No. 2002-172735 filed on Jun. 13, 2002 and PCT ApplicationNo. PCT/JP03/07567 filed on Jun. 13, 2003, the contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polytrimethylene terephthalate resin.More particularly, the present invention is concerned with apolytrimethylene terephthalate resin comprised mainly of trimethyleneterephthalate recurring units, which has the following characteristics:an intrinsic viscosity of from 0.8 to 4.0 dl/g; a molecular weightdistribution (Mw/Mn) of from 2.0 to 2.7; a psychometric lightnessL-value (L-1) of from 70 to 100 and a psychometric chroma b*-value(b*-1) of from −5 to 25; and a psychometric lightness L-value (L-2) offrom 70 to 100 and a psychometric chroma b*-value (b*-2) of from −5 to25 as measured after heating the polytrimethylene terephthalate resin at180° C. for 24 hours in air. By using the polytrimethylene terephthalateresin of the present invention, a shaped article having high strengthand excellent color can be stably produced on a commercial scale.Further, the present invention is also concerned with a method forstably producing the polytrimethylene terephthalate resin with highproductivity on a commercial scale.

2. Prior Art

A polytrimethylene terephthalate resin (hereinafter, referred to as“PTT”) not only has characteristics similar to those of a nylon (e.g.,soft feeling due to the low elasticity of the resin, excellent elasticrecovery and good dyeability), but also has characteristics similar tothose of a polyethylene terephthalate (hereinafter, referred to as“PET”) (e.g., wash and wear property, dimensional stability anddiscoloration resistance). Therefore, a PTT has been attractingattention as a raw material which can be used for producing carpets,clothes, shaped articles and the like.

For further expanding the application fields of a PTT, it has beendesired to improve the strength and color of the fibers and shapedarticles of a PTT.

For improving the strength of the fibers and shaped articles of apolymer, it is necessary to increase the polymerization degree of thepolymer, and to narrow the molecular weight distribution of the polymerso as to reduce the amount of low molecular weight components in thepolymer. Further, for improving the color of the fibers and shapedarticles of a polymer, it is necessary not only to improve the whitenessof the polymer, but also to improve the heat resistance of the polymerso as to prevent the discoloration of the polymer, which is caused bythe thermal history experienced by the polymer during the drying,melting and the like.

As a polymerization method for producing a PTT, a melt polymerizationmethod is widely known. For example, Unexamined Japanese PatentApplication Laid-Open Specification No. Hei 5-262862 (corresponding toU.S. Pat. No. 5,340,909), WO98/23662, WO01/14450 and WO01/14451 disclosea method in which a melt polymerization is performed using apolymerization vessel equipped with a stirrer. The above-mentionedpolymerization vessel has advantages in that it exhibits excellentvolume efficiency and has a simple structure. Such a polymerizationvessel can be used on a small scale for efficiently performing apolymerization to produce a polymer having a high polymerization degree.However, when the above-mentioned polymerization vessel is used forperforming a polymerization on a commercial scale, the depth of theliquid reaction mixture in the polymerization vessel inevitably becomesdeep, leading to a marked occurrence of heat decomposition of thepolymer. Thus, a polymer having high polymerization degree cannot beproduced on a commercial scale.

Various techniques have been proposed for producing a PTT having a highpolymerization degree by melt polymerization. Examples of suchtechniques include a technique in which a lower alcohol diester ofterephthalic acid and trimethylene glycol are subjected to atransesterification reaction and a polycondensation reaction in thepresence of a titanium compound, wherein the molar ratio of the loweralcohol diester of terephthalic acid to trimethylene glycol is in therange of from 1/1.2 to 1/1.8 (Unexamined Japanese Patent ApplicationLaid-Open Specification No. Sho 51-140992); a technique in which anorganometal catalyst is used as a polycondensation catalyst, and anorganic sulfonic acid or an aliphatic carboxylic acid is used as acatalyst auxiliary (U.S. Pat. No. 4,611,049); a technique in which a tincatalyst is used as a polycondensation catalyst (Unexamined JapanesePatent Application Laid-Open Specification No. Hei 5-262862(corresponding to U.S. Pat. No. 5,340,909)); a technique in which aspecific titanium catalyst is used as a polycondensation catalyst(Unexamined Japanese Patent Application Laid-Open Specification Nos.2000-159875 and 2000-159876); a technique in which an antimony compoundis used as a polycondensation catalyst (Chemical Fiber InternationalVol. 46, pp 263–264, 1996); a technique in which heat decomposition of aPTT is suppressed by using a hindered phenol-type stabilizer having aspecific structure (Unexamined Japanese Patent Application Laid-OpenSpecification No. Sho 51-142097); and a technique in which theby-production of acrolein (formed by heating of a prepolymer and apolymer in air during the polymerization) is suppressed by blocking theterminals of the prepolymer and the polymer with a phosphorus-containingstabilizer and a hindered phenol-type stabilizer (WO98/23662 andWO99/11709). However, the above-mentioned techniques are disadvantageousin that the molecular weight of the obtained PPT is not satisfactorilyhigh, in that a lowering of the molecular weight of the PTT occursduring the molding thereof, and/or in that a discoloration of the PTToccurs. Thus, by the above-mentioned techniques, a PTT havingsatisfactory properties cannot be obtained.

Further, a method is proposed in which, for the purpose of obtaining ahigh molecular weight PTT which exhibits excellent heat stability duringthe spinning of the PTT, a solid-phase polymerization of a PTTprepolymer having a relatively low molecular weight is performed, inwhich the PTT prepolymer has not suffered heat decomposition and hasexcellent color (Unexamined Japanese Patent Application Laid-OpenSpecification No. Hei 8-311177, Japanese Patent Applicationprior-to-examination Publication (Tokuhyo) No. 2000-502392 and KoreanPatent No. 1998-061618). However, the solid-phase polymerizationproceeds while releasing trimethylene glycol (hereinafter, referred toas “TMG”) from the surface of pellets of the prepolymer during thepolymerization reaction. Therefore, the polymerization degree variesdepending on the size and shape of the pellets, and also variesdepending on the position in the pellets. Therefore, the PTT obtained bythis method is markedly non-uniform with respect to the polymerizationdegree. Further, in the solid-phase polymerization, the pellets of thesolid prepolymer get rubbed with one another over a long period of time,thereby generating a polymer powder which becomes a loss. Furthermore,in the above-mentioned method, the solid-phase polymerization should beconducted after the production of the prepolymer by the meltpolymerization and the like, and thus, the entire process for producinga PTT becomes complicated and costly. Still further, the presence of thepolymer powder in the spinning process causes breakage or fuzzing ofpolymer fibers. For removing the polymer powder, an addition steptherefor becomes necessary.

As a method for producing a PTT having a high polymerization degree onlyby melt polymerization, a technique has been proposed in which thepolymerization is performed using a disc ring reactor or a cage typereactor (WO00/64962) or a disc and donut conductor (U.S. Pat. No.5,599,900) to withdraw the TMG efficiently from the reaction system.However, each of the above-mentioned apparatuses is a horizontalagitation-type polymerizer which is equipped with a rotary driving part.Therefore, in the above-mentioned method, when a polymerization isperformed under a high vacuum for obtaining a polymer having a highpolymerization degree, it is impossible to seal the driving partcompletely. Thus, it is impossible to prevent the intrusion of a traceamount of oxygen into the polymer, and hence, a, discoloration of thepolymer inevitably occurs. Especially, in the case of a PTT, suchdiscoloration markedly occurs. When the driving part is sealed with asealing liquid, it is likely that the sealing liquid gets mixed with thepolymer, thereby lowering the quality of the resultant PTT. Further,even when the driving part of the apparatus is tightly sealed at thestart of the operation thereof, the tightness of the sealing is loweredduring the operation conducted for a long period of time. Thus, theabove-mentioned method also has a serious problem with respect to themaintenance of the apparatuses.

On the other hand, a method for producing a resin (other than PTT) isknown in which the polymerization apparatus used therein does not have arotary driving part, and a polymerization is performed by allowing aprepolymer to fall from a perforated plate (free-fall polymerizationmethod).

For example, a method is disclosed in which a polyester prepolymer isallowed to fall in the form of fibers in vacuo in an attempt to obtain apolyester having a desired molecular weight (U.S. Pat. No. 3,110,547).In this method, a polymerization reaction is performed in a one passmode without recycling the polymer, because the recycling of a polymerwhich has already been allowed to fall in the form of fibers causes thelowering of the quality of the final polyester. However, theabove-mentioned method has the following disadvantages. The polymer inthe form of fibers are easily broken during the polymerization reaction,thereby causing a disadvantageously large variation in quality of thefinal condensation polymer products. In addition, a low molecular weightcondensation polymer is scattered from the polymer fibers during thepolymerization reaction to stain the lower surface of the perforatedplate. Due to such staining of the lower surface of the perforatedplate, it becomes difficult to cause the polymer to fall in the form offibers, so that the polymer fibers contact with one another to causebreakage of the polymer fibers or the polymer fibers are combinedtogether to form a thick fiber in which the reaction does not proceedefficiently.

In order to solve these problems, various methods have been proposed.Examples of such methods include a method in which a polyester or apolyamide is produced by allowing a prepolymer to fall along and incontact with the surface of a perforated guide or a wire guide, which isvertically arranged in a reaction vessel, so that the polymerization ofthe prepolymer is effected during the fall thereof (Examined JapanesePatent Application Publication No. Sho 48-8355 and Unexamined JapanesePatent Application Laid-Open Specification No. Sho 53-17569); a methodfor continuously condensation-polymerizing bis-(β-hydroxyalkyl)terephthalate (which is an initial-stage condensation product ofpolyethylene terephthalate (PET)), in which bis-(β-hydroxyalkyl)terephthalate is allowed to fall along and in contact with wire guidesin an atmosphere of inert gas, wherein the wire guides are hungvertically from the holes of a perforated plate, so that thepolymerization of bis-(β-hydroxyalkyl) terephthalate is effected duringthe fall thereof (Examined Japanese Patent Application Publication No.Hei 4-58806); and a method for producing a melt-polycondensationpolymer, such as a polyester, a polyamide and a polycarbonate, in whicha melt-polycondensation prepolymer is caused to absorb an inert gas, andthen, polymerized under reduced pressure (WO99/65970 which alsodiscloses an apparatus used in the method).

However, each of the above patent documents only describes a method forproducing a polyester, such as a PET, or nylon, and has no proposal orsuggestion about the production of a PTT. As a result of the studies ofthe present inventors, it has been found that, when any of theabove-mentioned methods are simply applied to the production of a PTT(that is, when the production of a PTT is conducted by theabove-mentioned methods, using raw materials and conditions which areconventionally used in the production of a PTT), a foaming of a polymervigorously occurs, thereby staining the lower surface of the perforatedplate or the inner wall of the reaction vessel having the guidesprovided therein. A PTT is susceptible to heat decomposition, ascompared to a PET. Therefore, the stain caused by the above-mentionedvigorous foaming of the polymer is easily decomposed. When the resultantdecomposition products get mixed with the polymer, disadvantages arecaused in that the quality of the polymer is lowered, in that thedesired polymerization degree cannot be obtained, and in that theobtained PTT suffers discoloration. Further, the simple application ofthe above-mentioned methods to the production of PTT is accompanied byproblems in that it is difficult to achieve a satisfactorily highpolymerization degree, and in that the final PTT contains low molecularweight polymers, which result in a broad molecular weight distributionof the final polymer and are likely to lower the mechanical strength ofan ultimate shaped article.

As mentioned above, the conventional methods for producing a PTT havethe following problems:

-   (1) It is difficult to produce a PTT having a high polymerization    degree only by melt polymerization (i.e., without solid-phase    polymerization) on a commercial scale. When the production of a PTT    is conducted by solid-phase polymerization, disadvantages are caused    in that the molecular weight distribution of the obtained PTT    becomes too broad, and in that the production process becomes    complicated and costly (due to the loss caused by the formation of    polymer powder).-   (2) When it is attempted to produce a PTT having high polymerization    degree by using a specific catalyst or stabilizer, the obtained    polymer is likely to suffer heat decomposition and discoloration.

With respect to the free-fall method (in which a polymerization isperformed by allowing a prepolymer to fall freely in the form of fibersfrom a perforated plate) and the guide-wetting fall method (in which apolymerization is performed by allowing a prepolymer to fall along andin contact with a guide), it is known that these methods can be used forproducing polyamide and polyesters (such as a PET) other than a PTT.However, the application of the above-mentioned methods to theproduction of a PTT is not known, and a PTT having satisfactoryproperties cannot be obtained by a simple application of these methodsto the production of a PTT which is different from the above-mentionedpolyamides and other polyesters with respect to the melt viscosity, andresistance to heat decomposition, and volatilities of by-products.

For these reasons, there has been a demand for the development of amethod which can be used for producing an excellent PTT having a highpolymerization degree on a commercial scale, which PTT can be used forstably producing a shaped article having excellent strength and color.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view toward solving the above-mentionedproblems accompanying the prior art techniques. As a result, it hasunexpectedly been found that, by polymerizing a molten form of aspecific trimethylene terephthalate prepolymer by the so-called“guide-wetting fall process” at a temperature of from the crystallinemelting point of the prepolymer to 290° C., it becomes possible toproduce a specific excellent polytrimethylene terephthalate resin whichcan be used for stably producing a shaped article exhibiting excellentstrength and color. The above-mentioned specific polytrimethyleneterephthalate resin is composed mainly of recurring units oftrimethylene terephthalate, and has the following characteristics: anintrinsic viscosity [η] of from 0.8 to 4.0 dl/g; a molecular weightdistribution (Mw/Mn) of from 2.0 to 2.7; a psychometric lightnessL-value (L-1) of from 70 to 100 and a psychometric chroma b*-value(b*-1) of from −5 to 25; and a psychometric lightness L-value (L-2) offrom 70 to 100 and a psychometric chroma b*-value (b*-2) of from −5 to25 as measured after heating the polytrimethylene terephthalate resin at180° C. for 24 hours in air. The present invention has been completed,based on these novel findings.

Accordingly, it is an object of the present invention to provide apolytrimethylene terephthalate resin which can be used for stablyproducing a shaped article having excellent strength and color on acommercial scale.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following description and appendedclaims taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows an explanatory diagrammatic view of an example of areaction vessel which can be used in the present invention;

FIG. 2 shows explanatory diagrammatic views of examples of an inert gasabsorption device and a reaction vessel, which can be used in thepresent invention; and

Each of FIGS. 3 to 6 is an explanatory diagrammatic view of one form ofa production system used for practicing the method of the presentinvention.

DESCRIPTION OF REFERENCE CHARACTERS AND NUMERALS

-   A: Polytrimethylene terephthalate prepolymer-   B: Polytrimethylene terephthalate resin-   C: Mixture of raw materials (including a starting monomer, a    reactant monomer, a catalyst, an additive and the like)-   D: Exhaust gas-   E: Inert gas-   1, 14, 18, 28, 32, N2 and N7: Transferring pump-   2: Inlet for prepolymer A-   3, N4: Perforated plate-   4: Observing window-   5, N5: Guide-   5′: Polymer falling along and in contact with the guide-   6: Inlet for gas-   7, 13, 17, 21, 24, 27 and 31: Vent-   8: Withdrawal pump for polymer 5′-   9: Outlet for polymer 5′-   10: Polymerizer-   11: Esterification reaction vessel-   12, 16, 20, 23, 26 and 30: Agitation element-   15: First vertical agitation type polymerizer-   19: Second vertical agitation type polymerizer-   22: Horizontal agitation type polymerizer-   25: First transesterification reaction vessel-   29: Second transesterification reaction vessel-   N1: Inert gas absorption device-   N3: Inlet for raw materials-   N6: Inlet for inert gas

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided apolytrimethylene terephthalate resin comprising:

90 to 100 mole % of trimethylene terephthalate recurring units, and

0 to 10 mole % of at least one monomer unit selected from the groupconsisting of monomer units obtained from comonomers which are otherthan the monomers used for forming the trimethylene terephthalaterecurring units and which are copolymerizable with at least one of themonomers used for forming the trimethylene terephthalate recurringunits, the polytrimethylene terephthalate resin having the followingcharacteristics (A) to (D):

(A) an intrinsic viscosity [η] of from 0.8 to 4.0 dl/g;

(B) a molecular weight distribution of from 2.0 to 2.7 in terms of theMw/Mn ratio, wherein Mw represents the weight average molecular weightof the polytrimethylene terephthalate resin and Mn represents the numberaverage molecular weight of the polytrimethylene terephthalate resin;

(C) a psychometric lightness L-value (L-1) of from 70 to 100 and apsychometric chroma b*-value (b*-1) of from −5 to 25; and

(D) a psychometric lightness L-value (L-2) of from 70 to 100 and apsychometric chroma b*-value (b*-2) of from −5 to 25 as measured afterheating the polytrimethylene terephthalate resin at 180° C. for 24 hoursin air.

For easy understanding of the present invention, the essential featuresand various preferred embodiments of the present invention areenumerated below.

-   1. A polytrimethylene terephthalate resin comprising:

90 to 100 mole % of trimethylene terephthalate recurring units, and

0 to 10 mole % of at least one monomer unit selected from the groupconsisting of monomer units obtained from comonomers which are otherthan the monomers used for forming the trimethylene terephthalaterecurring units and which are copolymerizable with at least one of themonomers used for forming the trimethylene terephthalate recurringunits,

the polytrimethylene terephthalate resin having the followingcharacteristics (A) to (D):

(A) an intrinsic viscosity [η] of from 0.8 to 4.0 dl/g;

(B) a molecular weight distribution of from 2.0 to 2.7 in terms of theMw/Mn ratio, wherein Mw represents the weight average molecular weightof the polytrimethylene terephthalate resin and Mn represents the numberaverage molecular weight of the polytrimethylene terephthalate resin;

(C) a psychometric lightness L-value (L-1) of from 70 to 100 and apsychometric chroma b*-value (b*-1) of from −5 to 25; and

(D) a psychometric lightness L-value (L-2) of from 70 to 100 and apsychometric chroma b*-value (b*-2) of from −5 to 25 as measured afterheating the polytrimethylene terephthalate resin at 180° C. for 24 hoursin air.

-   2. The polytrimethylene terephthalate resin according to item 1    above, wherein the polytrimethylene terephthalate resin has an    intrinsic viscosity [η] of from 1.25 to 2.5 dl/g.-   3. The polytrimethylene terephthalate resin according to item 1 or 2    above, which has a terminal carboxyl group content of from 0 to 20    meq/kg.-   4. The polytrimethylene terephthalate resin according to any one of    items 1 to 3 above, which has a molecular weight distribution of    from 2.0 to 2.6.-   5. The polytrimethylene terephthalate resin of any one of items 1 to    4 above, which is in the form of pellets.-   6. The polytrimethylene terephthalate resin according to item 5    above, wherein the pellets have an average weight of from 1 to 1000    mg per pellet, and wherein the pellets contains a powder of the    polytrimethylene terephthalate resin in an amount of 0 to 0.5% by    weight, based on the total weight of the pellets, which powder    passes through a 30-mesh filter and does not pass through a 300-mesh    filter.-   7. The polytrimethylene terephthalate resin according to item 5 or 6    above, wherein the pellets have a crystallinity (X_(c)) of 40% or    less, wherein the crystallinity is defined by the following formula:    X _(c)(%)={ρ_(c)×(ρ_(s)−p_(a))}/{ρ_(s)×(ρ_(c)−ρ_(a))}×100    -   wherein ρ_(a) is 1.300 g/cm³ which is an amorphous density of        trimethylene terephthalate homopolymer, ρ_(c) is 1.431 g/cm³        which is a crystal density of trimethylene terephthalate        homopolymer, and ρ_(s) represents a density (g/cm³) of the        pellets.-   8. A method for producing a polytrimethylene terephthalate resin,    which comprises:

(1) providing a molten form of a trimethylene terephthalate prepolymercomprising:

90 to 100 mole % of trimethylene terephthalate recurring units, and

0 to 10 mole % of at least one monomer unit selected from the groupconsisting of monomer units obtained from comonomers which are otherthan the monomers used for forming the trimethylene terephthalaterecurring units and which are copolymerizable with at least one of themonomers used for forming the trimethylene terephthalate recurringunits,

the trimethylene terephthalate prepolymer having an intrinsic viscosity[η] of from 0.2 to 2 dl/g, and

(2) polymerizing the molten form of a trimethylene terephthalateprepolymer at a temperature which is equal to or higher than thecrystalline melting point of the prepolymer and is not higher than 290°C. under reduced pressure by the guide-wetting fall process in which theprepolymer is allowed to fall along and in contact with the surface of aguide so that polymerization of the prepolymer is effected during thefall thereof.

-   9. The method according to item 8 above, wherein the molten    prepolymer is continuously fed to a polymerization reaction zone for    effecting the polymerization of the prepolymer in the step (2) and    the resultant polytrimethylene terephthalate resin produced in the    step (2) is continuously withdrawn from the polymerization zone, so    that the step (2) for prepolymer polymerization is continuously    performed.-   10. The method according to item 8 or 9 above, wherein the guide has    at least one portion selected from the group consisting of a concave    portion, a convex portion and a perforated portion.-   11. The method according to any one of items 8 to 10 above, wherein    the prepolymer falling along and in contact with the surface of the    guide is in a foaming state.-   12. The method according to any one of items 8 to 11 above, wherein    the polymerization in the step (2) is performed, while introducing    inert gas to the polymerization reaction zone.-   13. The method according to item 12 above, wherein the amount of the    inert gas introduced to the polymerization reaction zone is in the    range of from 0.05 to 100 mg per gram of the polytrimethylene    terephthalate resin withdrawn from the polymerization reaction zone.-   14. The method according to item 12 or 13 above, wherein at least a    part of the inert gas is introduced to the polymerization reaction    zone, independently from the feeding of the trimethylene    terephthalate prepolymer to the polymerization reaction zone.-   15. The method according to any one of items 12 to 14 above, wherein    at least a part of the inert gas is introduced to the polymerization    reaction zone in such a form as absorbed or contained in the    trimethylene terephthalate prepolymer.-   16. The method according to any one of items 8 to 15 above, wherein    the prepolymer has an intrinsic viscosity [η] of from 0.5 to 2.0    dl/g and a terminal carboxyl group ratio of 50% or less in terms of    the molar ratio (%) of the terminal carboxyl groups of the    prepolymer to all terminal groups of the prepolymer.-   17. The method according to any one of items 8 to 16 above, wherein    the prepolymer is produced by at least one polymerization method    selected from the following methods (a) to (d):

(a) a polymerization method using a vertical agitation type polymerizer;

(b) a polymerization method using a horizontal agitation typepolymerizer;

(c) a polymerization method using a free-fall polymerizer having aperforated plate; and

(d) a polymerization method using a thin film type polymerizer.

-   18. The method according to item 17 above, wherein the prepolymer is    produced by the method (b).-   19. A polytrimethylene terephthalate resin produced by the method of    any one of items 8 to 18 above.

Hereinbelow, the present invention is described in detail.

The polytrimethylene terephthalate resin of the present inventioncomprises:

90 to 100 mole % of trimethylene terephthalate recurring units, and

0 to 10 mole % of at least one monomer unit selected from the groupconsisting of monomer units obtained from comonomers which are otherthan the monomers used for forming the trimethylene terephthalaterecurring units and which are copolymerizable with at least one of themonomers used for forming the trimethylene terephthalate recurringunits.

The trimethylene terephthalate recurring units are formed by reacting aterephthalic acid material with a trimethylene glycol material. Examplesof terephthalic acid materials include terephthalic acid, and diestersof terephthalic acid, such as dimethyl terephthalate. Examples oftrimethylene glycol materials include 1,3-propanediol, 1,2-propanediol,1,1-propanediol, 2,2-propanediol, and a mixture thereof. From theviewpoint of stability, 1,3-propanediol is especially preferred as atrimethylene glycol material.

Examples of the above-mentioned comonomers include ester-formingmonomers, such as 5-sulfoisophthalic acid sodium salt,5-sulfoisophthalic acid potassium salt,4-sulfo-2,6-naphthalenedicarboxylic acid sodium salt, 3,5-dicarboxylicacid benzenesulfonic acid tetramethylphosphonium salt, 3,5-dicarboxylicacid benzenesulfonic acid tetrabutylphosphonium salt, 3,5-dicarboxylicacid benzenesulfonic acid tributylmethylphosphonium salt,3,6-dicarboxylic acid naphthalene-4-sulfonic acid tetrabutylphosphoniumsalt, 3,6-dicarboxylic acid naphthalene-4-sufonic acidtetramethylphosphonium salt, 3,5-dicarboxylic acid benzenesulfonic acidammonium salt, 3,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentylglycol, 1,5-pentamethyleneglycol, 1,6-hxamethylene glycol,heptamethylene glycol, octamethylene glycol, decamethylene glycol,dodecamethylene glycol, 1,4-cyclohexanediol, 1,3-cyclohexanediol,1,2-cyclohexanediol, 1,4-cyclohexanedimethanol,1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, oxalic acid,malonic acid, succinic acid, gultaric acid, adipic acid, heptanedioicacid, octanedioic acid, sebacic acid, dodecanedioic acid,2-methylgultaric acid, 2-methyladipic acid, fumaric acid, maleic acid,itaconic acid, 1,4-cyclohexanedicarboxylic acid,1,3-cyclohexanedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid.

The polytrimethylene terephthalate resin of the present invention mayfurther comprise: cyclic or chain oligomers other than polytrimethyleneterephthalate resin; monomers, such as dimethyl terephthalate(hereinafter, referred to as “DMT”), terephthalic acid (hereinafter,referred to as “TPA”) and trimethylene glycol (hereinafter, referred toas “TMG”); and/or any of various additives, such as a delustering agent,a thermal stabilizer and a flame retardant.

For obtaining a fiber or a shaped article, which has excellent strengthand color, and which is aimed at in the present invention, it isnecessary not only to improve the polymerization degree of thepolytrimethylene terephthalate resin while narrowing the distribution ofpolymerization degree, but also to improve the whiteness of the resinwhile improving the resistance of the resin against the discoloration athigh temperatures.

As a yardstick of the polymerization degree, the intrinsic viscosity [η]can be used. For obtaining the above-mentioned excellent fiber or shapedarticle, which has excellent strength, it is necessary that the resin(used for producing the fiber or shaped article) have an intrinsicviscosity of 0.8 dl/g or more. On the other hand, from the viewpoint ofimproving the moldability of the resin and the ease in measuring theamount of the resin in a gear pump, the intrinsic viscosity should notbe too high. For this reason, it is necessary that the intrinsicviscosity [η] be 4.0 dl/g or less. The intrinsic viscosity [η] ispreferably in the range of from 1.05 to 3.0 dl/g, more preferably from1.25 to 2.5 dl/g, still more preferably from 1.3 to 2.0 dl/g.

Further, for improving the strength of the above-mentioned fiber orshaped article, not only should the average polymerization degree behigh, but also the amount of a low molecular weight polymer should below, namely, the molecular weight distribution should be narrow. In thepresent invention, the molecular weight distribution is expressed interms of a value (Mw/Mn) which is calculated by dividing the weightaverage molecular weight (Mw) by the number average molecular weight(Mn), wherein each of Mw and Mn is measured by gel permeationchromatography. In the present invention, it is necessary that the Mw/Mnvalue be 2.7 or less. The Mw/Mn value is preferably 2.6 or less, morepreferably 2.5 or less, still more preferably 2.4 or less. In general,the lower limit of the molecular weight distribution of a condensationpolymer is 2.

With respect to the color of the polytrimethylene terephthalate resin,for suppressing the darkening of the ultimate shaped article and forenabling the resin to exhibit a desired color by the use of a dye or apigment, it is necessary that the polytrimethylene terephthalate resinhave a psychometric lightness L-value (L-1) of 70 or more and apsychometric chroma b*-value (b*-1) of −5 or more. From the viewpoint ofsuppressing the discoloration of the resin by heat decomposition, it isnecessary that the polytrimethylene terephthalate resin have apsychometric chroma b*-value of 25 or less. There is no particularlimitation with respect to the upper limitation of the (L-1) value, butin general, it is 100. The (L-1) value is preferably 75 or more, morepreferably 80 or more. The (b*-1) value is preferably from −3 to 15,more preferably from −2 to 10.

Further, from the studies of the present inventors, it has been foundthat, for improving the whiteness of the ultimate shaped article, apolytrimethylene terephthalate resin used for producing a shaped articleshould exhibit not only excellent whiteness, but also excellentresistance to discoloration during the heating of the resin (e.g.,during the high temperature drying, melt molding or the like of theresin). The reason for this is not clear, but it is presumed that thediscoloration of the resin is caused by not only the thermaldecomposition of the resin per se, but also certain substances orfunctional groups which are inevitably contained in the polytrimethyleneterephthalate resin. It is considered that the above-mentionedsubstances or functional groups are formed by heat decomposition of aprepolymer (used in the production of the polytrimethylene terephthalateresin) and/or the polytrimethylene terephthalate resin. However,especially when the below-mentioned polymerization method proposed bythe present inventors is employed, it is possible to obtain apolytrimethylene terephthalate resin which has excellent resistance tothe discoloration during the heating. The reason for this is consideredas follows. The proposed method is advantageous not only in that theleakage of oxygen into the polymerization reaction system can besuppressed, thereby preventing the formation of the above-mentionedsubstances and functional groups, but also in that the surface area ofthe prepolymer being polymerized in the polymerizer employed in thismethod is extremely large as compared to the case of polymerizers whichare conventionally employed for the production of a polytrimethyleneterephthalate resin, and the surface of the prepolymer is efficientlyrenewed, so that the above-mentioned substances or functional groups, ifany, can be easily withdrawn from the reaction system.

As a yardstick of the susceptibility to discoloration by heat, the colorof a polytrimethylene terephthalate resin after heating at 180° C. for24 hours in air can be used. In the present invention, thepolytrimethylene terephthalate resin heated under the above-mentionedconditions needs to have a psychometric lightness L-value (L-2) of 70 ormore, and a psychometric chroma b*-value (b*-2) of from −5 to 25. Thepsychometric lightness L-value (L-2) is preferably 75 or more, morepreferably 80 or more. The psychometric chroma b*-value (b*-2) ispreferably from −4 to 21, more preferably from −3 to 18, still morepreferably from −2 to 16.

In the present invention, for preventing the hydrolysis of thepolytrimethylene terephthalate resin even when the shaping of the resinwhich has not been fully dried is performed, and for improving theweatherability of a shaped article of the polytrimethylene terephthalateresin, it is preferred that the polytrimethylene terephthalate resin ofthe present invention has a terminal carboxyl group content of not morethan 30 meq/kg (based on the weight of the polytrimethyleneterephthalate resin). The terminal carboxyl group content is preferablynot more than 20 meq/kg, more preferably not more than 15 meq/kg, stillmore preferably not more than 10 meq/kg. It is preferred that theterminal carboxyl group content is as small as possible.

The polytrimethylene terephthalate resin of the present invention can beused, for example, for producing an extrusion-molded article, such as afilm or a sheet. In the production of such an extrusion-molded article,it is desired that the polytrimethylene terephthalate resinsimultaneously satisfies all of such requirements as a very highmolecular weight, a very narrow molecular weight distribution and a verylow terminal carboxyl group content. Therefore, it is preferred that thepolytrimethylene terephthalate resin for use in the production of anextrusion-molded article has an intrinsic viscosity [η] of from 1.25 to2.5 dl/g, an Mw/Mn ratio of 2.6 or less and a terminal carboxyl groupcontent of 20 meq/kg or less; it is more preferred that the resin has anintrinsic viscosity [η] of from 1.30 to 2.0 dl/g, an Mw/Mn ratio of 2.5or less and a terminal carboxyl group content of 15 meq/kg or less; andit is still more preferred that the resin has an intrinsic viscosity [η]of from 1.30 to 2.0 dl/g, an Mw/Mn ratio of 2.4 or less and a terminalcarboxyl group content of 10 meq/kg or less. When the production of thepolytrimethylene terephthalate resin is conducted by the below-mentionedpolymerization method proposed by the present inventors, thepolymerization rate is high and the surface area of the prepolymer beingpolymerized is large. Therefore, not only can the polymerization degreebe improved, but also the terminal carboxyl group content can be loweredto a level which has never been achieved by the conventional meltpolymerization. Further, in this method, the polymerization degree canbe improved while maintaining a high piston flowability (the “highpiston flowability” means a property that the flowing resin in thepolymerizer has no local variation of the flow rate, i.e., the flowingresin as a whole has a uniform flow rate). Thus, by the proposed method,it is possible to obtain a polytrimethylene terephthalate resin having anarrow molecular weight distribution, i.e., a resin which does notcontain polymers having largely different molecular weights. When apolytrimethylene terephthalate resin is produced by solid-phasepolymerization, the resin produced exhibits a high polymerizationdegree. However, in the solid-phase polymerization, the polymerizationdegree varies depending on the reaction site in the pellets (i.e.,whether the reaction site is at an inner portion or outer portion of thepellets), and also varies depending on the size and shape of thepellets, so that it is very difficult to obtain a polymer having anarrow molecular weight distribution. By the proposed polymerizationmethod, it has, for the first time, become possible to produce apolytrimethylene terephthalate resin which can be suitably used for thecommercial scale production of the above-mentioned extrusion-moldedarticle.

The polytrimethylene terephthalate resin of the present invention, whichis in a molten form obtained immediately after the production thereof,can be spun or shaped. Alternatively, the resin can be formed intopellets, and then re-melted at the time of spinning or shaping of theresin.

When the resin is used in the form of pellets, it is desired that theamount of loss is small, and that the pellets can be extruded uniformlyby means of an extruder. Therefore, it is preferred that each pellet hasan appropriate size, and that the amount of polymer powder adhering tothe surface of the pellets is small.

In the present invention, it is preferred that the average weight ofpellets is from 1 to 1,000 mg per pellet. The pellets having such anaverage weight is advantageous in that uniform extrusion of the pelletsby means of a extrusion molding machine becomes easy, that the pelletscan be handled with ease at the time of transportation, drying andspinning thereof, and that the drying rate of the pellets becomes fast.The average weight of the pellets is more preferably from 5 to 500 mgper pellet, still more preferably from 10 to 200 mg per pellet. Withrespect to the shape of the pellet, there is no particular limitation,and the shape of the pellet may be any of a sphere, a rectangle, acylinder and a cone. However, from the viewpoint of ease in handling ofthe pellets, it is preferred that the length of the largest portion ofeach pellet is 15 mm or less, more advantageously 10 mm or less, stillmore advantageously 5 mm or less.

With respect to the polymer powder adhering to the surface of thepellets, it is preferred that the amount of the polymer powder is in therange of from 0 to 0.5% by weight, based on the total weight of thepellets, which powder passes through a 30-mesh filter and does not passthrough a 300-mesh filter. When the amount of the polymer powder is 0.5%by weight or less, not only is the loss decreased, but also it becomespossible to prevent the clogging of a pneumatic line (i.e., pipe line inwhich pellets are transferred by gas) or a filter of an air-exhaustventilator attached to a dryer, and to suppress the pressure variationin an extruder during the spinning, molding or compounding, so thatultimate products having a uniform quality can be easily obtained. It ispreferred that the amount of the polymer powder is as small as possible.From a practical point of view, the amount of the polymer powder ispreferably in the range of from 0 to 0.2% by weight, more preferablyfrom 0 to 0.1% by weight, still more preferably from 0 to 0.05% byweight, based on the total weight of the pellets.

Further, it is preferred that the pellets have a crystallinity (X_(c))of 0 to 40%, wherein the crystallinity is defined by the followingformula:X _(c)(%)={ρ_(c)×(ρ_(s)−ρ_(a))}/{ρ_(s)×(ρ_(c)−ρ_(a))}×100

-   -   wherein ρ_(a) is 1.300 g/cm³ which is an amorphous density of        trimethylene terephthalate homopolymer, ρ_(c) is 1.431 g/cm³        which is a crystal density of trimethylene terephthalate        homopolymer, and ρ_(s) represents a density (g/cm³) of the        pellets.

The above-mentioned crystal density of trimethylene terephthalatehomopolymer (1.431 g/cm³) is a theoretical value which is calculatedfrom the number of crystal lattices of trimethylene terephthalatehomopolymer. The above crystal density value (1.431 g/cm³) is describedin “Poritorimechirenterefutareto no Kesshoudanseiritsu (Crystalelasticity of polytrimethylene terephthalate)” (“Zairyou (Material)”,written by Katsuhiko Nakamae, Vol. 35, No. 396, p. 1067, 2000). Further,the amorphous density of trimethylene terephthalate homopolymer (1.300g/cm³) is obtained by measuring the density of a sample amorphouspolymer obtained by quenching a trimethylene terephthalate homopolymerin a molten form. (With respect to the sample polymer, it can beconfirmed that the sample polymer is amorphous, when no crystal peak isobserved in the analysis of the sample polymer by X-ray diffractometry.)

When the pellets have the above-mentioned crystallinity, it becomespossible to prevent a problem which is unique to a PTT and is unlikelyto arise in the case of other polyesters, such as a PET and a PBT(polybutylene terephthalate), i.e., a problem that pellets becomebrittle and generate a large amount of polymer powder during thetransportation of the pellets by means of a pneumatic conveyor or afeeder. It is preferred that the crystallinity is from 0 to 35%, moreadvantageously from 0 to 30%.

In the present invention, the crystallinity of a pellet means an averagevalue of crystallinity values measured at different portions of thepellet. Specifically, for example, it is preferred that, when a surfaceportion of the pellet is cut away from a central portion of the pelletand crystallinities of these portions are measured, both of the surfaceportion and the central portion are in the above-mentioned crystallinityrange. Further, it is preferred that the difference in crystallinitybetween the surface portion and the central portion is 40% or less, moreadvantageously 30% or less, still more advantageously 20% or less.

For obtaining pellets having the above-mentioned crystallinity, it ispreferred that a polytrimethylene terephthalate in a molten form, whichis obtained by polymerization, is extruded into a strand or a sheet,and, subsequently, the obtained strand or sheet is immersed in acoolant, such as water, to cool the strand or sheet, followed by cuttingof the strand or sheet to obtain pellets. It is preferred that thetemperature of the coolant is 20° C. or less, more advantageously 15° C.or less, still more advantageously 10° C. or less. From the viewpoint ofeconomy and ease in handling of the pellets, it is preferred to usewater as a coolant. Naturally, the temperature of water as a coolant is0° C. or more. It is preferred that the cutting to obtain pellets isperformed with respect to the strand or sheet solidified by cooling theextruded strand or sheet to 55° C. or lower within 120 seconds after theextrusion.

Hereinbelow, the method for producing the polytrimethylene terephthalateresin of the present invention is described in detail.

The method for producing the polytrimethylene terephthalate resin of thepresent invention comprises the following steps (1) and (2):

(1) providing a molten form of a trimethylene terephthalate prepolymercomprising:

90 to 100 mole % of trimethylene terephthalate recurring units, and

0 to 10 mole % of at least one monomer unit selected from the groupconsisting of monomer units obtained from comonomers which are otherthan the monomers used for forming the trimethylene terephthalaterecurring units and which are copolymerizable with at least one of themonomers used for forming the trimethylene terephthalate recurringunits, the trimethylene terephthalate prepolymer having an intrinsicviscosity [η] of from 0.2 to 2 dl/g, and

(2) polymerizing the molten form of a trimethylene terephthalateprepolymer at a temperature which is equal to or higher than thecrystalline melting point of the prepolymer and is not higher than 290°C. under reduced pressure by the guide-wetting fall process in which theprepolymer is allowed to fall along and in contact with the surface of aguide so that polymerization of the prepolymer is effected during thefall thereof.

As mentioned above, a polymerizer which does not have a rotary drivingpart has been proposed as a polymerizer for producing resins other thana polytrimethylene terephthalate. However, the melt-polycondensationreaction for producing a polytrimethylene terephthalate greatly differsfrom the melt-polycondensation reactions for producing other types ofpolyesters, such as a PET and a PBT, and for producing polyamides.Therefore, a practical production of a polytrimethylene terephthalatecannot be realized simply by employing the polymerizers which have beenused for the production of the other types of polyesters and for theproduction of polyamides. The important differences between thepolytrimethylene terephthalate, and polyamides and the other types ofpolyesters (such as a PET and a PBT) are explained below.

Firstly, both of the melt-polycondensation reaction for producingpolyamides and the melt-polycondensation reaction for producing theother types of polyesters are equilibrium reactions. However, theequilibrium constants of the above two reactions greatly differ fromeach other. In general, the equilibrium constants of themelt-polycondensation reactions for producing polyamides are in theorder of 10², whereas the equilibrium constants of themelt-polycondensation reactions for producing the other types ofpolyesters is approximately 1. Thus, despite that both of the reactionsfor producing polyamides and the reactions for producing the other typesof polyesters are polycondensation reactions, the equilibrium constantsof the reactions for producing the other types of polyesters areextremely small as compared to those of the reaction for producing thepolyamides. When an equilibrium constant of a certain reaction is large,the reaction proceeds even without efficiently withdrawing a by-productfrom the reaction system. Therefore, it is easy to increase thepolymerization degrees of polyamides. With respect to the other types ofpolyesters (such as a PET and a PBT), although the equilibrium constantsof the reactions for producing a PET and a PBT are small, theby-products can be easily withdrawn from the reaction systems, so thatit is also easy to increase the polymerization degree of each of a PETand a PBT. The reason for this is as follows. In the case of a PET, thePET has a satisfactory heat stability, and hence, a polymerizationreaction for producing the PET can be performed at a temperature(generally from 280 to 300° C.) which is much higher than the boilingpoint (198° C.) of ethylene glycol which is a by-product of thepolymerization reaction. By performing the polymerization at such a hightemperature, the vapor pressure of ethylene glycol can be increased and,hence, the ethylene glycol can be easily withdrawn from the reactionsystem. Also in the case of a PBT, 1,4-butanediol, which is a by-productof the polymerization reaction for producing a PBT, can be easilywithdrawn from the reaction system. The reason for this has not yet beenelucidated, but is considered as follows. In the polymerization reactionsystem for producing a PBT, 1,4-butanediol (which is a by-product havinga high boiling point) is converted into low boiling point substances,such as tetrahydrofuran (formed by hydrolysis) and butadiene (formed byheat decomposition), which low boiling point substances can be easilywithdrawn from the reaction system.

As in the case of the polymerization reactions for producing the othertypes of polyesters, the polymerization reaction for producing apolytrimethylene terephthalate has a low equilibrium constant, andhence, the by-produced trimethylene glycol (TMG) needs to be efficientlywithdrawn from the reaction system so as to advance the polymerizationreaction. The TMG has a boiling point as high as 214° C. On the otherhand, the polytrimethylene terephthalate is susceptible to heatdecomposition, so that the polymerization reaction for producing thepolytrimethylene terephthalate needs to be performed at a lowtemperature. Therefore, it is difficult to withdraw the TMG from thereaction system. Further, when the polymerization degree of apolytrimethylene terephthalate becomes high, the following disadvantageis caused. The viscosity of the polytrimethylene terephthalate alsobecomes high and, hence, it becomes difficult to withdraw TMG from thereaction system. In such a case, a heat decomposition of thepolytrimethylene terephthalate markedly occurs, so that the reactionrate is lowered, and then, the polymerization degree of thepolytrimethylene terephthalate starts to be lowered. If thepolymerization reaction is performed at a high temperature, thewithdrawal of the TMG becomes easier; however, the heat decomposition ofthe polytrimethylene terephthalate markedly occurs, thereby leading tothe above-mentioned disadvantage that, when the polymerization degree ofa polytrimethylene terephthalate becomes high and the viscosity of thepolytrimethylene terephthalate also becomes high, the reaction rate islowered, and then, the polymerization degree of the polytrimethyleneterephthalate starts to be lowered.

However, as a result of the studies of the present inventors, it hasunexpectedly been found that, when a molten form of a polytrimethyleneterephthalate prepolymer having an intrinsic viscosity within theabove-mentioned specific range is polymerized by the above-mentionedguide-wetting fall process at an appropriate temperature under reducedpressure, a polytrimethylene terephthalate can be produced withoutcausing the problems accompanying the conventional polymerizationmethods for producing the other types of polyesters, such as a PET, andfor producing polyamides, i.e., methods in which a polymerization isperformed by allowing a prepolymer to fall in the form of fibers or tofall along and in contact with a guide, such as a wire.

With respect to the guide-wetting fall process, reference can be made,for example, to U.S. Pat. Nos. 5,589,564, 5,840,826, 6,265,526 and6,320,015.

The features of the method of the present invention are described below.

Firstly, for obtaining a polytrimethylene terephthalate resin having ahigh polymerization degree only by melt polymerization, it is requirednot only to suppress the heat decomposition of the PTT, but also toremove efficiently a TMG (by-product of the reaction for producing thePTT). In the method of the present invention, these requirements aresatisfied by performing the polymerization by allowing a prepolymer tofall along and in contact with the guide at an appropriate temperatureunder reduced pressure to thereby increase the surface area of theprepolymer. Further, by allowing the polymer to fall along and incontact with a guide, it becomes possible to prevent the disadvantageousfluctuation of qualities of the products, wherein the fluctuation occursdue to the breakage of the polymer flow in the polymerizer.

Secondly, for preventing the discoloration of the polymer which iscaused by the entrance of oxygen and a sealing liquid into the polymer,it is required to employ a polymerizer having no rotary driving part ata portion of the polymerizer, which portion contains a gaseous phaseduring the polymerization. In the guide-wetting fall process, there isno need for the polymerizer to have a rotary driving part in such agaseous phase portion of the polymerizer, and the polymerizer exhibitsan excellent sealability under a highly vacuumized condition, so that adiscoloration caused by leakage of oxygen into the polymerizer can bealmost completely prevented. Further, since the polymerizer has norotary driving part, a mixing of a sealing liquid into a polymer wouldnot occur, and the maintenance of the polymerizer is easy. Thus, a highquality polytrimethylene terephthalate which is free from adisadvantageous discoloration can be obtained.

Thirdly, for stably producing a polytrimethylene terephthalate resin ona commercial scale, it is required to suppress the foaming of theprepolymer introduced into the polymerization reaction zone, so as toprevent the staining of the lower surface of the perforated plate andinner wall of the polymerizer. In the method of the present invention,this requirement is satisfied by introducing a prepolymer having anincreased viscosity, more specifically by polymerizing a prepolymerhaving a high intrinsic viscosity within a specific range at a specificlow temperature. By virtue of this feature, it becomes possible tosuppress the lowering of the quality of the polytrimethyleneterephthalate resin, which is caused by the mixing or entrance of thestain into the polytrimethylene terephthalate resin.

Thus, by the method of the present invention, the problems accompanyingthe conventional techniques for performing a melt-polycondensation toproduce a polytrimethylene terephthalate resin can be solved, and itbecomes possible to produce resin which is free from a discolorationcaused by heat decomposition, and which has high quality and highpolymerization degree. Such effects are unexpected from the conventionaltechniques for performing polymerization reactions for producingpolyamides and the other types of polyesters.

In the present invention, it is necessary to introduce a trimethyleneterephthalate prepolymer in a molten form through the holes of theperforated plate into the polymerization reaction zone at a temperaturewhich is equal to or higher than the crystalline melting point of theprepolymer and is not higher than 290° C., wherein the prepolymer has anintrinsic viscosity [η] of from 0.2 to 2 dl/g.

In the present invention, the “trimethylene terephthalate prepolymer”means a polycondensation product which has a molecular weight lower thanthe final polytrimethylene terephthalate resin obtained therefrom.

In the present invention, it is important to suppress the scattering ofthe prepolymer in the polymerization reaction zone, which is caused bythe vigorous foaming of the prepolymer. In the present invention, forsuppressing the scattering of the prepolymer, and for effectivelyremoving the by-produced TMG from the reaction system, it is essentialto introduce the above-mentioned prepolymer having a specific intrinsicviscosity [η] into the polymerization reaction zone at theabove-mentioned specific temperature. When the scattering of theprepolymer is caused by the vigorous foaming of the prepolymerintroduced through the holes of the perforated plate into thepolymerization reaction zone, the polymer adheres to the lower surfaceof the perforated plate and the inner wall of the polymerizer, therebystaining them. The prepolymer which adheres to the lower surface of theperforated plate and the inner wall of the polymerizer remains in thepolymerizer for a long period of time, and hence, suffers heatdecomposition to form a discolored low molecular weight product and/or adiscolored modified product. When such discolored products get mixedwith the final polytrimethylene terephthalate resin, the quality of theresin is lowered. For suppressing the scattering of the prepolymercaused by the vigorous foaming thereof, it is necessary that theprepolymer has an intrinsic viscosity [η] of 0.2 or more. Further, forconstantly producing a resin having a narrow molecular weightdistribution, it is preferred that the prepolymer has a high viscosity.The reason for this is as follows. In the guide-wetting fall processemployed in the present invention, a fluctuation of polymerizationdegree of the prepolymer being polymerized may occur due to thefluctuation of the falling rate of the prepolymer and the fluctuation ofthe level of surface renewal of the prepolymer, leading to a broadmolecular weight distribution of the final resin. For preventing suchfluctuation of the falling rate of the prepolymer and fluctuation of thelevel of surface renewal of the prepolymer, it is preferred that theviscosity of the prepolymer is high.

However, on the other hand, when the prepolymer has too high anintrinsic viscosity, it becomes difficult to withdraw efficiently theby-produced TMG from the reaction system. Further, when the intrinsicviscosity is too high, the amount of the by-produced TMG becomesextremely small, so that it becomes difficult to cause an appropriatelymild foaming of the prepolymer during the fall thereof in thepolymerizer, which foaming of the prepolymer is an important feature ofthe polymerization method of the present invention. Thus, it becomesdifficult to improve the polymerization degree of the polytrimethyleneterephthalate resin.

For preventing the above disadvantages, it is necessary that theprepolymer has an intrinsic viscosity [η] of 2 dl/g or less. It ispreferred that the prepolymer has an intrinsic viscosity [η] of from 0.3to 1.8 dl/g, more advantageously from 0.4 to 1.5 dl/g.

In addition, for preventing disadvantages (e.g., vigorous foaming of theprepolymer, and heat decomposition of the prepolymer) which are causedby the low viscosity of the prepolymer and which lead to a lowering ofthe quality of the polytrimethylene terephthalate resin, it is necessarythat the temperature of the prepolymer introduced into thepolymerization reaction zone be 290° C. or less. On the other hand, foruniformly introducing the prepolymer into the polymerization reactionzone without solidifying the prepolymer in the holes of the perforatedplate, and for causing the prepolymer as a whole to fall uniformly alongand in contact with the guide without partially solidifying theprepolymer during the fall thereof, it is necessary that the temperatureof the prepolymer introduced into the polymerization reaction zone beequal to or higher than the crystalline melting point of the prepolymer.

In the present invention, the crystalline melting point of theprepolymer means a temperature at which an endothermic peak ascribed tothe melting of a crystal is observed in a differential scanningcalorimetry (DSC) chart of the prepolymer, wherein the DSC chart isobtained by means of an input compensation-type differential scanningcalorimeter (trade name: Pyris 1; manufactured and sold by Perkin Elmer,Inc., U.S.A.) under the following conditions:

Measuring temperature: 0 to 280° C., and

Rate of temperature elevation: 10° C./min.

The temperature of the prepolymer introduced into the polymerizationreaction zone is preferably 5° C. or more higher than the crystallinemelting point of the prepolymer and not higher than 280° C., morepreferably 10° C. or more higher than the crystalline melting point ofthe prepolymer but not higher than 275° C., still more preferably 15° C.or more higher than the crystalline melting point of the prepolymer butnot higher than 265° C.

In the present invention, the above-mentioned perfirated plate is aplate having a plurality of through-holes through which the prepolymeris introduced into the polymerization reaction zone. There is noparticular limitation with respect to the thickness of the perforatedplate. However, the thickness of the perforated plate is generally inthe range of from 0.1 to 300 mm, preferably from 1 to 200 mm, morepreferably from 5 to 150 mm. The perforated plate needs to have astrength sufficient to sustain the pressure inside the chamber of thepolymerizer, into which the molten prepolymer is fed. Also, when theguide(s) in the polymerization reaction zone of the polymerizer is (are)hung from the perforated plate, it is necessary that the perforatedplate can sustain the weight of the guide(s) and the molten prepolymerwhich is falling along and in contact with the surface of the guide(s).For this reason, it is preferred that the perforated plate is reinforcedwith a rib. The shape of the hole of the perforated plate is generallyselected from a circle, an ellipse, a triangle, a slit, a polygon, astar and the like. The area at the opening of each hole is generally inthe range of from 0.01 to 100 cm², preferably from 0.05 to 10 cm², morepreferably from 0.1 to 5 cm². Further, nozzles or the like may beattached to the holes of the perforated plate. The distance betweenmutually adjacent holes of the perforated plate is generally from 1 to500 mm, preferably from 25 to 100 mm, as measured between the respectivecenters of the mutually adjacent holes. The perforated plate may havetubes attached thereto, such that the hollow portions of the tubes serveas the holes of the perforated plate. Further, the hole of theperforated plate may have a tapered configuration. It is preferred thatthe size and shape of the hole are determined so that the pressure losswhich occurs when the molten form of a prepolymer passes through theperforated plate is from 0.01 to 5 MPa, more preferably from 0.1 to 5MPa. When the pressure loss is in the above-mentioned range, it becomeseasy to obtain a resin having a further improved polymerization degree(the reason for this is not clear). In general, it is preferred that thematerial used for the perforated plate is selected from the groupconsisiting of metallic materials, such as stainless steel, carbonsteel, Hastelloy, nickel, titanium, chromium and alloys other thanmentioned.

Further, it is preferred that a filter is provided in the flowing pathof the prepolymer in the polymerizer at a point which is upstream of theperforated plate. The reason for this is that the filter can be used forremoving an impurity, if any, which is contained in the prepolymer, andwhich may cause the clogging of the holes of the perforated plate. Thetype of filter is appropriately selected so that the impurity having asize larger than the diameter of the holes of the perforated plate canbe removed, and that the filter is not destroyed by the passage of theprepolymer therethrough.

Examples of methods for causing the molten prepolymer to pass downwardlythrough a perforated plate provided in the polymerizer and fall alongand in contact with the guide include a method in which the prepolymeris allowed to fall only by liquid head or by gravity, and a method inwhich the prepolymer on the perforated plate is pressurized by using apump or the like to thereby force the molten prepolymer to passdownwardly through a perforated plate. It is preferred that thefluctuation of the amount of falling prepolymer is suppressed by meansof a pump which has a measuring ability, such as a gear pump.

There is no particular limitation with respect to the number of holes ofthe perforated plate. The appropriate number of holes of the perforatedplate varies depending on the polymerization conditions (such as apolymerization temperature and a polymerization pressure), the amount ofthe catalyst used, the range of the molecular weight of the prepolymer,and the like. For example, when it is intended to produce the resin at arate of 100 kg/hr, it is preferred that the perforated plate has 1 to10⁴ holes, more advantageously 2 to 10² holes.

In the present invention, it is necessary that the prepolymer which hasbeen introduced through the holes of the perforated plate into thepolymerization reaction zone is polymerized by allowing the prepolymerto fall along and in contact with the guide in the polymerizationreaction zone under reduced pressure. It is preferred that theprepolymer in the polymerization reaction zone is in a foaming statesuch that the bubbles formed in the prepolymer in the polymerizationreaction zone would not be broken instantaneously. It is especiallypreferred that the prepolymer at a lower portion of the guide is in afoaming state. Needless to say, it is most preferred that the whole ofthe prepolymer in the polymerization reaction zone is in a foamingstate.

The guide used in the method of the present invention may be any of awire, a chain, a wire mesh (each of the chain and the wire mesh is madeby combining wires), a jungle gym-like body (having a lattice structurecomposed of wires), a flat or curved thin plate, a perforated plate, anda filler column (which is formed by regularly or irregularly pilingfillers together).

For efficiently withdrawing TMG from the reaction system, it ispreferred that the surface area of the falling prepolymer is increased.Therefore, it is preferred that the guide is a wire, a chain, a wiremesh or a jungle gym-like body. Further, for more efficientlywithdrawing TMG from the reaction system to further improve thepolymerization rate, it is especially preferred not only to increase thesurface area of the guide, but also to form concave portion(s) and/orconvex portion(s) on the surface of the guide which are arranged alongthe length thereof, so as to promote the agitation and surface renewalof the prepolymer falling along and in contact with the surface of theguide. Thus, it is preferred that the guide has at least one portionselected from the group consisting of a concave portion, a convexportion and a perforated portion. Specifically, it is preferred to use aguide having a structure which hampers the fall of the polymer, such asa chain, a jungle gym-like body or a wire having concavo-convex portionson the surface thereof along which the prepolymer falls. Needless tosay, the above-mentioned guides can be used in combination.

In the present specification, the term “wire” means a body in which theratio of the length of the body to the average perimeter of thecross-section of the body is very large. There is no particularlimitation with respect to the cross-sectional area of the wire.However, in general, the cross-sectional area is in the range of from10⁻³ to 10² cm², preferably from 10⁻² to 10² cm², more preferably from10⁻¹ to 1 cm². There is no particular limitation with respect to theshape of the cross-section of the guide, and the shape is generallyselected from a circle, an ellipse, a triangle, a quadrangle, a polygon,a star and the like. The shape of the cross-section of the wire may beuniform or may vary along the length of the wire. The wire may behollow. Further, the wire may be made of a single strand, or made of aplurality of strands, wherein, for example, the strands are twistedtogether. The surface of the wire may be smooth or may haveconcavo-convex portions as mentioned above, a locally protruding portionor the like. There is no particular limitation with respect to thematerial used for the wire, but the material is generally selected fromthe group consisting of, for example, stainless steel, carbon steel,Hastelloy, nickel, titanium, chromium and other alloys. If desired, thewire may be subjected to surface treatment. Examples of surfacetreatments include plating, lining, passivation, and washing with anacid.

The “wire mesh” means a body which is made by combining theabove-mentioned wires so as to form a lattice. The wires can be linearor curved, and the angle between the combined wires can be appropriatelyselected. With respect to the area ratio of the wires of the wire meshto the open spaces (which ratio is measured with respect to theprojected image of the wire mesh), there is no particular limitation,but the area ratio is generally in the range of from 1/0.5 to 1/1,000,preferably from 1/1 to 1/500, more preferably from 1/5 to 1/100. It ispreferred that the area ratio of the wire mesh does not varyhorizontally relative to the vertical direction of the wire mesh.Further, it is preferred that the area ratio of the wire mesh along thevertical length of the wire mesh does not vary or varies such that, whenthe wire mesh is provided as the guide in the polymerizer, the area ofeach open space at a lower portion of the wire mesh becomes smaller thanthat at an upper portion of the wire mesh (which means that the arearatio at a lower portion of the wire mesh becomes larger than that at anupper portion of the wire mesh).

In the present invention, the “chain” means a body in which rings formedby the above-mentioned wires are linked together. The shape of rings canbe a circle, an ellipse, a rectangle, a square or the like. The ringscan be linked in one dimension, two dimensions or three dimensions.

In the present invention, the term “jungle gym-like body” means amaterial in which the above-mentioned wires are three-dimensionallycombined with one another so as to form a lattice. The wires used can belinear or curved, and the angle between the combined wires can beappropriately selected.

Examples of wires having convex portion(s) and/or concave portion(s) onthe surface thereof (along and in contact with which the prepolymer isallowed to fall) include a wire to which a rod having a circular orpolygonal cross-section is attached such that the rod extendssubstantially vertically of the wire, and a wire to which a disc-shapedor cylindrical-shaped body is attached such that the wire penetratesthrough the disc-shaped or cylindrical-shaped body around the centerthereof. It is preferred that the convex portion has a height which isat least 5 mm larger than the diameter of the wire. As a specificexample of wires having convex portion(s), there can be mentioned a wireto which a plurality of discs are attached at intervals of from 1 to 500mm, in which each disc has a diameter which is at least 5 mm larger thanthe diameter of the wire and not more than 100 mm, and a thickness offrom approximately 1 to 10 mm.

With respect to the chain, jungle gym-like body and wire havingconcavo-convex portions on the surface thereof, which are used as theguides, there is no particular limitation on the volume ratio of theskeleton of the guide (e.g., wires used to form the guide) to the openspaces in the guide. However, in general, the volume ratio is in therange of from 1/0.5 to 1/10⁷, preferably from 1/10 to 1/10⁶, morepreferably from 1/10² to 1/10⁵. It is preferred that the volume ratiodoes not vary horizontally of the downwardly extending guide. Further,it is preferred that the volume ratio of the downwardly extending guidealong the length of the guide does not vary or varies such that, whenthe guide is provided in the polymerizer, the volume ratio at a lowerportion of the guide becomes larger than that at an upper portion of theguide.

The above-mentioned guides can be used individually or in combination,depending on the configuration of the guides. When the guide is a wireor a linear chain, the number of guide(s) used is generally in the rangeof from 1 to 100,000, preferably from 3 to 50,000. When the guide is awire mesh, a chain formed by two-dimensionally combining the wires, athin plate or a perforated plate, the number of guide(s) used isgenerally in the range of from 1 to 1,000, preferably from 2 to 100.When the guide is a chain formed by three-dimensionally combining thewires, a jungle gym-like body or a filler column, the number of theguide(s) can be appropriately selected depending on the sizes of thepolymerizer and the polymerization reaction zone where the guide(s) is(are) provided.

When a plurality of guides are used, it is preferred to arrange theguides so as for the guides not to contact with each other by using aspacer or the like.

In the present invention, in general, the prepolymer is introducedthrough at least one hole of the perforated plate into thepolymerization reaction zone where the prepolymer is allowed to fallalong and in contact with the guide. The number of holes of theperforated plate can be appropriately selected depending on the shape ofthe guide. In the method of the present invention, the prepolymer whichhas passed through a single hole of the perforated plate can be allowedto fall along and in contact with a plurality of guides. However, forcausing the prepolymer to fall uniformly so as to obtain a resin havinga narrow molecular weight distribution constantly, it is preferred thatthe number of guide(s) along which the prepolymer (which has passedthrough a single hole of the perforated plate) is allowed to fall issmall. For example, when the guide is a wire, it is preferred that thenumber of guide(s) along which the prepolymer (which has passed througha single hole of the perforated plate) is allowed to fall is 3 or less.There is no particular limitation with respect to the position of theguide(s) in the polymerizer so long as the prepolymer can fall along andin contact with the guide(s), and the guide(s) can be provided such thatthe guide passes through the hole of the perforated plate or is hungbelow the hole of the perforated plate.

With respect to the distance over which the molten prepolymer (havingpassed through the holes of the perforated plate) falls along and incontact with the surface of the guide, the distance is preferably from0.3 to 50 m, more preferably from 0.5 to 20 m, still more preferablyfrom 1 to 10 m.

The flow rate of prepolymer passing through the holes of the perforatedplate is preferably in the range of from 10⁻² to 10⁻² liters/hr per holeof the perforated plate, more preferably from 0.1 to 50 liters/hr perhole of the perforated plate. When the flow rate of prepolymer is withinthe above-mentioned range, it becomes possible to prevent a markedlowering of the polymerization rate and the productivity of the finalresin.

In the method of the present invention, it is preferred that the averagefalling time of the prepolymer is in the range of from 10 seconds to 100hours, more preferably from 1 minute to 10 hours, still more preferablyfrom 5 minutes to 5 hours, most preferably from 20 minutes to 3 hours.

In the method of the present invention, as mentioned above, it isnecessary that the polymerization reaction (performed by allowing theprepolymer to fall along and in contact with the guide) be performedunder reduced pressure. By performing the polymerization reaction underreduced pressure, TMG (which is by-produced during the polymerizationreaction) is efficiently withdrawn from the reaction system so as toadvance the polymerization reaction. The reduced pressure means apressure which is lower than the atmospheric pressure. Generally, it ispreferred that the polymerization is conducted under a pressure of100,000 Pa or less, more preferably 10,000 Pa or less, still morepreferably 1,000 Pa or less, most preferably 100 Pa or less. There is noparticular limitation with respect to the lower limit of the pressureunder which the polymerization is conducted. However, from the viewpointof the size of the equipment for reducing the pressure in the reactionsystem, it is preferred that the pressure is 0.1 Pa or more.

Further, an inert gas which does not adversely affect the polymerizationreaction can be introduced into the reaction system under reducedpressure, so as to remove the by-produced TMG in such a form asentrained by the inert gas. In the method of the present invention, theinert gas is generally used in an amount of from 0.005 to 100 mg pergram of the polytrimethylene terephthalate resin withdrawn from thepolymerization reaction zone.

Conventionally, it has been understood that the introduction of inertgas into a polycondensation reaction system lowers the partial pressureof a by-product formed during the polycondensation reaction, therebydisplacing the equilibrium of the reaction in the direction of thedesired product formation. However, in the present invention, the inertgas is introduced into the reaction zone only in a very small amount,and hence, the improvement of the polymerization rate by the lowering ofpartial pressure of a by-product cannot be expected. Thus, from theconventional understanding, the function of the inert gas used in themethod of the present invention cannot be explained. From the studies ofthe present inventors, it has surprisingly been found that theintroduction of inert gas into the polymerization reaction zone causesan appropriately mild foaming of the molten prepolymer on the guide, sothat not only is the surface area of the molten prepolymer greatlyincreased, but also the surface renewal of the prepolymer vigorouslyoccurs without staining the inner wall of the polymerizer. It ispresumed that a vigorous movement of the prepolymer at various portions(including inner and surface portions) thereof causes the remarkableimprovement in the polymerization rate.

As the inert gas introduced into the polymerization reaction zone, it ispreferred to use inert gas which does not cause discoloration,denaturation or decomposition of the polymer. Preferred examples ofinert gases include nitrogen gas, argon gas, helium gas, carbon dioxidegas and a lower hydrocarbon gas. Needless to say, a mixture of the abovementioned gases can also be used in the present invention. As the inertgas, it is more preferred to use nitrogen gas, argon gas, helium gasand/or carbon dioxide gas. Among these gases, nitrogen gas is mostpreferred from the view-point of availability.

In the present invention, the amount of inert gas introduced into thepolymerization reaction zone may be very small. Specifically, it ispreferred that the amount of inert gas is in the range of from 0.05 to100 mg per gram of the final resin withdrawn from the polymerizationreaction zone. By using the inert gas in an amount of 0.05 mg or moreper gram of the final resin withdrawn from the polymerization reactionzone, it becomes possible to foam the polymer satisfactorily so as toincrease the polymerization degree. On the other hand, by using theinert gas in an amount of 100 mg or less, it becomes easy to maintainthe appropriate reduced pressure in the polymerization reaction zone. Itis preferred that the amount of inert gas introduced into thepolymerization reaction zone is in the range of from 0.1 to 50 mg pergram of the final resin withdrawn from the polymerization reaction zone,more advantageously from 0.2 to 10 mg.

Examples of methods for introducing the inert gas into thepolymerization reaction zone include a method in which at least a partof the inert gas is introduced to the polymerization reaction zone,independently from the feeding of the trimethylene terephthalateprepolymer to the polymerization reaction zone, and a method in which atleast a part of the inert gas is introduced to the polymerizationreaction zone in such a form as absorbed and/or contained in thetrimethylene terephthalate prepolymer, such that the inert gas is causedto be discharged from the prepolymer under reduced pressure in thepolymerization reaction zone. These two methods can be used individuallyor in combination.

In the present invention, it is preferred to employ the above-mentionedmethod in which at least a part of the inert gas is introduced to thepolymerization reaction zone in such a form as absorbed by thetrimethylene terephthalate prepolymer or in such a form as contained inthe trimethylene terephthalate prepolymer. The former means that theinert gas is dissolved in the prepolymer, and is not present in the formof bubbles in the prepolymer. On the other hand, the latter means thatthe inert gas is present in the form of bubbles in the prepolymer. Whenthe inert gas is present in the form of bubbles in the prepolymer, it ispreferred that the size of each bubble is as small as possible. It ispreferred that the average diameter of each bubble is 5 mm or less, moreadvantageously 2 mm or less.

When the inert gas is introduced to the polymerization reaction zone,independently from the feeding of the prepolymer to the polymerizationreaction zone, it is preferred to feed the inert gas to the polymerizerat a position remote from the perforated plate and close to the outletfor withdrawing the final resin. Further, it is preferred to feed theinert gas to the polymerizer at a position remote from the vent to whicha vacuum gas discharge line is connected.

On the other hand, examples of methods for causing the inert gas to beabsorbed by and/or contained in the prepolymer include a method usingany of conventional absorption devices, such as a packed column typeabsorption device, a tray-containing column type absorption device, aspraying device-containing column type absorption device (in which aliquid is sprayed in a gas to be absorbed in the liquid), a turbulentcontact absorption device, a gas-liquid film cross-contacting typeabsorption device, a high-speed rotary flow type absorption device, anabsorption device utilizing mechanical force, which are described in“Kagaku Souchi Sekkei-Sousa Shiriizu No. 2, Kaitei Gasu Kyushu (Designand Operation of Chemical Devices, No. 2, Gas Absorption (RevisedVersion))”, pp. 49–54 (published on March 15, 1981 by Kagaku Kogyosha,Inc., Japan); and a method in which the inert gas is injected into theprepolymer in a conduit for transferring the prepolymer to thepolymerizer. Most preferred is a method using a device in which theprepolymer is allowed to fall along and in contact with the surface of aguide in an atmosphere of inert gas to thereby cause the prepolymer toabsorb the inert gas during the fall thereof. In this method, inert gashaving a pressure higher than the pressure inside the polymerizer isintroduced into the gas absorption device. The pressure of the inert gasintroduced into the gas absorption device is preferably from 0.01 to 1MPa, more preferably from 0.05 to 0.5 MPa, still more preferably from0.1 to 0.2 MPa.

In both of the above-mentioned methods for introducing the inert gasinto the polymerization reaction system, it is preferred that at least apart of the prepolymer falling in the polymerization reaction zone is ina foaming state. It is especially preferred that the prepolymer at alower portion of the polymerization reaction zone is a forming state.Needless to say, it is most preferred that the whole of the prepolymerfalling in the polymerization reaction zone is in a foaming state. Inthe present invention, the “foaming state” encompasses both a state inwhich the formed bubbles are immediately broken and a state in which theformed bubbles are maintained for a relatively long time.

In the method of the present invention, it is necessary that thetemperature in the polymerization reaction zone is equal to or higherthan the crystalline melting point of the prepolymer, and not higherthan 290° C. By performing the polymerization reaction at a temperaturewhich is equal to or higher than the crystalline melting point of theprepolymer, it becomes easy to cause the prepolymer to fall stablywithout causing the prepolymer to get too viscose or solidified.Further, by performing the polymerization reaction at a temperaturewhich is not higher than 290° C., a discoloration of the prepolymercaused by heat decomposition of the prepolymer is suppressed, and hence,a polytrimethylene terephthalate resin having high quality can be easilyobtained. It is preferred that the difference between the temperature inthe polymerization reaction zone (which is within the above-mentionedrange) and the temperature of the molten prepolymer introduced into thepolymerization reaction zone through the perforated plate is 20° C. orless, more advantageously 10° C. or less, still more advantageously 5°C. or less, and it is most preferred that the temperature in thepolymerization reaction zone and the temperature of the moltenprepolymer introduced into the polymerization reaction zone are thesame. The temperature in the polymerization reaction zone can becontrolled by adjusting the temperature of a heater or a jacket which isprovided on the inner wall of the polymerizer, or by adjusting thetemperature of a heater or a heating medium which is provided inside theguide.

In the present invention, for improving the polymerization rate, it ispreferred that the prepolymer contains a polycondensation catalyst.

Examples of polycondensation catalysts include titanium alkoxides, suchas titanium tetrabutoxide and titanium tetraisopropoxide; titaniumcompounds, such as titanium dioxide and a double salt of titaniumdioxide and silicon dioxide; antimony compounds, such as diantimonytrioxide and antimony acetate; and tin compounds, such as butylstannate, butyltin tris(2-ethylhexoate) and tin 2-ethylhexanoate. Ofthese, titanium tetrabutoxide and tin 2-ethylhexanoate are especiallypreferred from the viewpoint of improvement in the polymerizationreaction rate and the color of the final resin. These catalysts can beused individually or in combination. It is preferred that thepolycondensation catalyst is contained in the prepolymer in an amount offrom 0.001 to 1% by weight, more advantageously from 0.005 to 0.5% byweight, still more advantageously from 0.01 to 0.2% by weight, based onthe weight of the prepolymer.

In the present invention, for obtaining a polytrimethylene terephthalateresin having a very high molecular weight, it is preferred that thepolymerization degree of the prepolymer is increased, and that theterminal carboxyl group ratio of the prepolymer is lowered, wherein theterminal carboxyl group ratio is a molar ratio (%) of the terminalcarboxyl groups at the terminals of the prepolymer to the total ofterminal groups of the prepolymer. It is preferred that the prepolymerhas an intrinsic viscosity [η] of 0.5 or more. By using a prepolymerhaving such a high intrinsic viscosity, it becomes possible to obtain adesirable falling rate of the prepolymer and a desirable foaming stateof the prepolymer, thereby greatly improving the polymerization rate. Itis preferred that the prepolymer has an intrinsic viscosity [η] of 0.55or more, more preferably 0.60 dl/g or more.

On the other hand, it is preferred that the prepolymer has a terminalcarboxyl group ratio of 50% or less. The terminal carboxyl group ratiois calculated by the following formula:

Terminal  carboxyl  group  ratio(%) = (terminal  carboxyl  group  content)/(total  terminal  group  content) × 100wherein:

the terminal carboxyl group content is the molar amount of carboxylgroup per kg of a sample, and

the total terminal group content is the total molar amount of terminalgroups per kg of a sample.

When the terminal carboxyl group ratio is 50% or less, thepolymerization reaction rate can be improved, so that a resin having ahigh molecular weight can be obtained and that a discoloration of theresin can be suppressed. The terminal carboxyl group ratio is morepreferably 30% or less, still more preferably 20% or less, mostpreferably 0%.

The above-mentioned prepolymer which is suitable for producing a resinhaving a high molecular weight has a high intrinsic viscosity.Therefore, when such a prepolymer is used, it becomes difficult not onlyto withdraw TMG from the reaction system due to the high viscosity ofthe prepolymer, but also to produce the prepolymer by means of aconventional vertical agitation type polymerizer. In addition, fordecreasing the terminal carboxyl group ratio of the prepolymer, it isnecessary to improve the polymerization rate and suppress heatdecomposition. Therefore, it is preferred that the prepolymer isproduced by means of a horizontal agitation type polymerizer equippedwith one or two stirrers, each having a large surface area and a highsurface renewal efficiency.

The method of the present invention can be practiced in either a mannerin which the prepolymer in a molten form is continuously fed into thepolymerizer and introduced into the polymerization reaction zone throughthe holes of the perforated plate, and the prepolymer in a molten formis allowed to fall along and in contact with the guide to therebyperform a polymerization, and all of the resultant resin is withdrawnform the polymerizer; or a manner in which a part of the resin (obtainedby the above-mentioned polymerization performed by allowing theprepolymer to fall along and in contact with the guide) is recycled tothe polymerizer and subjected to further polymerization. However, it ispreferred to employ the former (in which all of the obtained resin iswithdrawn from the polymerizer). When the method of the presentinvention is practiced in the above-mentioned manner in which a part ofthe obtained resin is recycled to the polymerizer and subjected tofurther polymerization, for suppressing the heat decomposition of theresin which occurs at a reservoir portion of the polymerizer (i.e., abottom portion of the polymerizer where the resin obtained by thepolymerization is accumulated) and a conduit for recycling of the resin,it is preferred to reduce the retention times and lower the temperaturesat the above-mentioned reservoir portion and conduit.

Hereinbelow, the method for producing a polytrimethylene terephthalateprepolymer which is used in the present invention is described indetail.

As representative examples of preferred methods for producing thepolytrimethylene terephthalate prepolymer on a commercial scale, thereare the following two methods which differ in the materials used. In oneof the methods, a lower alcohol diester of terephthalic acid and TMG aresubjected to transesterification reaction to obtainbis(3-hydroxylpropyl)terephthalate (hereinafter, referred to as “BHPT”)which is an intermediate of a PTT, and the obtained BHPT is subjected toa polycondensation reaction, thereby obtaining a PTT prepolymer(hereinafter, this method is referred to as a “transesterificationmethod”). In the other method, terephthalic acid and TMG are subjectedto an esterification reaction to obtain BHPT, and the obtained BHPT issubjected to a polycondensation reaction as in the above-mentionedtransesterification method, thereby obtaining a PTT prepolymer(hereinafter, this method is referred to as “direct esterificationmethod”).

Further, the production of the polytrimethylene terephthalate prepolymercan be performed in either a batchwise manner in which all of the rawmaterials are charged into the polymerizer at once and reacted togethersimultaneously to obtain a PTT prepolymer, or a continuous manner inwhich the raw materials are continuously fed into the polymerizer tocontinuously obtain a PTT prepolymer. In the present invention, it ispreferred that the production of the PTT prepolymer is performed in acontinuous manner, and that the resultant prepolymer is continuouslypolymerized by the method of the present invention.

In the present invention, the above-mentioned BHPT may contain unreactedraw materials (such as terephthalic acid, a lower alcohol diester ofterephthalic acid and TMG) and a PTT oligomer. However, it is preferredthat the BHPT comprises 70% by weight or more of the BHPT and/or a lowmolecular weight PTT oligomer, based on the total weight of the BHPT,and the above-mentioned unreacted raw materials and PTT oligomer.

Hereinbelow, explanations are made on some examples of the methods forobtaining the BHPT.

First, an explanation is made on the “transesterification method”. Inthe transesterification method, the BHPT is produced by subjectingdimethyl terephthalate (hereinafter, referred to as “DMT”) (which is alower alcohol diester of terephthalic acid) and TMG to atransesterification reaction at 150 to 240° C. in the presence of atransesterification catalyst. In the transesterification reaction, theDMT used as a raw material exhibits a high volatility, so that it ispreferred to use two or more reactors in combination, and to control thereaction temperature appropriately.

It is preferred that the lower alcohol diester of terephthalic acid andthe TMG are charged into the reactor in a molar ratio (a lower alcoholdiester of terephthalic acid/TMG molar ratio) of from 1/1.3 to 1/4, moreadvantageously from 1/1.5 to 1/2.5. When the amount of TMG is too smallso that the above-mentioned ratio is larger than 1/1.3, the reactiontime is likely to become disadvantageously long. Also when the amount ofTMG is too large so that the above-mentioned ratio is smaller than 1/4,the reaction time is likely to become disadvantageously long, because itbecomes necessary to volatilize the excess TMG.

In the transesterification method, it is necessary to use atransesterification catalyst. Preferred examples of transesterificationcatalysts include titanium alkoxides, such as titanium tetrabutoxide andtitanium tetraisopropoxide; tin compounds, such as tin 2-ethylhexanoate;cobalt acetate; calcium acetate; and zinc acetate. Among thesecatalysts, titanium tetrabutoxide and tin 2-ethylhexanoate are preferredbecause they function also as catalysts in the subsequentpolycondensation reaction to produce the final resin. The amount oftransesterification catalyst is preferably in the range of from 0.02 to1% by weight, more preferably from 0.05 to 0.5% by weight, still morepreferably from 0.08 to 0.2% by weight, based on the weight of thediester of terephthalic acid.

Next, an explanation is made on the “direct esterification method”. Inthe direct esterification method, the BHPT is produced by subjectingterephthalic acid and TMG to esterification reaction at 150 to 240° C.

It is preferred that the terephthalic acid and the TMG are charged intoa reactor in a molar ratio (terephthalic acid/TMG molar ratio) of from1/1.05 to 1/3, more preferably from 1/1.1 to 1/2. When the amount of TMGis too small so that the above-mentioned molar ratio is larger than1/1.05, the reaction time is likely to become disadvantageously long andthe resultant prepolymer is likely to be discolored. Also when theamount of TMG is too large so that the above-mentioned molar ratio issmaller than 1/3, the reaction time is likely to becomedisadvantageously long because it becomes necessary to volatilize theexcess TMG.

In the direct esterification method, free protons derived fromterephthalic acid function as a catalyst. Therefore, in the directesterification method, an esterification catalyst is not alwaysnecessary. However, for improving the reaction rate, it is preferred touse an esterification catalyst. Preferred examples of esterificationcatalysts include titanium alkoxides, such as titanium tetrabutoxide andtitanium tetraisopropoxide, and tin compounds, such as tin2-ethylhexanoate. It is preferred that the amount of esterificationcatalyst used is from 0.02 to 1% by weight, more preferably from 0.05 to0.5% by weight, still more preferably from 0.08 to 0.2% by weight, basedon the weight of terephthalic acid.

For advancing the esterification reaction smoothly, it is preferred toadd BHPT to a raw material mixture at the start of the reaction in anamount of 5 to 80% by weight, based on the total weight of the rawmaterial mixture and the BHPT. When the production of BHPT is performedin a batchwise manner, the esterification reaction can be initiated bysimultaneously charging the terephthalic acid and the TMG (rawmaterials) into a reactor. On the other hand, when the production ofBHPT is performed in a continuous manner, the esterification reactioncan be performed by continuously feeding a predetermined amount of amixture of terephthalic acid and TMG into a reactor to perform atransesterification reaction, while withdrawing a predetermined amountof the reaction product (BHPT) from the reactor.

The BHPT obtained by any of the above-mentioned methods is thensubjected to polycondensation, thereby obtaining the prepolymer used inthe present invention.

The production of the prepolymer by polycondensation is performed bysubjecting the BHPT to reaction at a predetermined temperature underreduced pressure or in an inert gas atmosphere, while withdrawingby-produced TMG from the reaction system.

It is preferred that such polycondensation reaction is performed at 230to 280° C. When the reaction is performed at a temperature lower than230° C., disadvantages are likely to occur that the formed prepolymergets solidified and that the reaction time becomes long. On the otherhand, when the reaction is performed at a temperature which is higherthan 280° C., a disadvantage is likely to occur that a vigorous heatdecomposition of the formed prepolymer occurs, and the resultantprepolymer cannot be used for producing a polymer having excellentcolor. It is preferred that the polycondensation reaction is performedat a temperature of from 232 to 275° C., more advantageously from 235 to270° C.

As mentioned above, the polycondensation reaction can be performed underreduced pressure or in an inert gas atmosphere. When the reaction isperformed under reduced pressure, the pressure is appropriatelycontrolled, taking into consideration the sublimation of the BHPT andpolycondensation product, and the reaction rate. When the reaction ispreformed in an inert gas atmosphere, it is important that the inside ofa reactor used is always satisfactorily purged with inert gas towithdraw the by-produced TMG efficiently from the reaction system.

When the BHPT is subjected to polycondensation, it is preferred to use apolycondensation catalyst. When a polycondensation catalyst is not used,the reaction time is likely to become disadvantageously long. Preferredexamples of polycondensation catalysts include titanium alkoxides, suchas titanium tetrabutoxide and titanium tetraisopropoxide; titaniumdioxide and a double salt of titanium dioxide and silicon dioxide;antimony compounds, such as diantimony trioxide and an antimony acetate;and tin compounds, such as butyl stannate, butyltin tris(2-ethylhexoate)and tin 2-ethylhexanoate. From the viewpoint of improving the reactionrate and color of the final resin, titanium tetrabutoxide and tin2-ethylhexanoate are especially preferred. The above-mentioned catalystscan be used individually or in combination. The amount ofpolycondensation catalyst used is preferably from 0.001 to 1% by weight,more preferably from 0.005 to 0.5% by weight, still more preferably from0.01 to 0.2% by weight, based on the weight of the prepolymer. When acompound which functions as a polycondensation catalyst is used in theproduction process of the BHPT, it is preferred that the total amount ofthe compounds capable of functioning as a polycondensation catalyst iswithin the above-mentioned range.

Examples of devices for conducting such polycondensation reactioninclude a vertical agitation type polymerizer, a horizontal agitationtype polymerizer equipped with one or two stirrers, a free-fall typethin film polymerizer having trays therein, and a thin film polymerizerin which the prepolymer is allowed to fall on a plane surface of anangled plate. Needless to say, these polymerizers can be used incombination.

When a polycondensation of BHPT is performed in a batchwise manner, asingle polymerizer can be employed from the start of thepolycondensation reaction through the completion of the polycondensationreaction. Needless to say, two or more polymerizers can be used. On theother hand, when a polycondensation of BHPT is performed in a continuousmanner, for effectively advancing the reaction, it is preferred toperform the reaction of from the polycondensation to the formation ofthe prepolymer in a stepwise manner, using two or more differentpolymerizers, wherein the two or more polymerizers are operated underdifferent temperature-pressure conditions.

In the present invention, if desired, various additives can beincorporated into the PTT resin by copolymerization or mixing. Examplesof additives include a delustering agent, a thermal stabilizer, a flameretardant, an antistatic agent, an anti-foaming agent, an orthochromaticagent, an antioxidant, an ultraviolet absorber, a nucleating agent and abrightener. These additives can be added at any time during theproduction of the PTT resin.

In the present invention, from the viewpoint of improving the whitenessand melt stability of the PTT resin, and suppressing the formation oforganic substances having a molecular weight of 300 or less, such asacrolein and an allyl alcohol, it is preferred that a stabilizer isadded at an appropriate stage of the production of the PTT resin, moreadvantageously before the polycondensation of BHPT.

Preferred examples of such stabilizers include pentavalent and/ortrivalent phosphorus compounds and hindered phenol compounds.

Examples of pentavalent and/or trivalent phosphorus compounds includetrimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenylphosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate,triphenyl phosphate, phosphoric acid and phosphorous acid. Among theabove-mentioned phosphorus compounds, trimethyl phosphate is especiallypreferred. It is preferred that the amount of phosphorus compound addedis in the range of from 2 to 250 ppm by weight, more advantageously from5 to 150 ppm by weight, still more advantageously from 10 to 100 ppm byweight, in terms of the weight of phosphorus atom contained in the PTT.

The hindered phenol compound is a phenol derivative which has asubstituent exhibiting a steric hindrance at a position adjacent to thephenolic hydroxyl group, and has at least one ester bond in itsmolecule.

Examples of hindered phenol compounds includepentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane,1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzene)isophthalic acid,triethylglycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)-propionate],1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],2,2-thio-diethylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate].

Among the above-exemplified hindered phenol compounds,pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]is preferred.

It is preferred that the amount of hindered phenol compound added is inthe range of from 0.001 to 1% by weight, more advantageously from 0.005to 0.5% by weight, still more advantageously from 0.01 to 0.1% byweight, based on the weight of the PTT resin. Needless to say, theabove-mentioned stabilizers can be used in combination.

Next, preferred examples of the polymerizer used in the method of thepresent invention are described below, referring to the drawings.

FIG. 1 shows an explanatory diagrammatic view of a specific example of apolymerizer used in the method of the present invention. In FIG. 1,trimethylene terephthalate prepolymer A is fed through inlet 2 intopolymerizer 10 by means of transferring pump 1. Then, prepolymer A isintroduced through perforated plate 3 into the interior (polymerizationreaction zone) of polymerizer 10, and is allowed to fall along and incontact with guides 5. The pressure in the interior (polymerizationreaction zone) of polymerizer 10 is controlled so as to maintain apredetermined reduced pressure. If desired, inert gas E, such asnitrogen, can be introduced into the polymerizer through inlet 6 for agas. TMG (which is distilled from the prepolymer) and inert gas E aredischarged as exhaust gas D from vent 7. The resultant PTT resin B iswithdrawn from the polymerizer by means of withdrawal pump 8 throughoutlet 9. Polymerizer 10 is heated by means of a heater or a jacket soas to maintain the temperature inside the polymerizer at a desiredlevel.

FIG. 2 shows explanatory diagrammatic views of specific examples of aninert gas absorption device and a polymerizer, which can be used in thepresent invention when the inert gas is introduced to the polymerizationreaction zone in such a form as absorbed or contained in the PTTprepolymer, and the inert gas is caused to be released from theprepolymer in the polymerization reaction zone under reduced pressure.In FIG. 2, PTT prepolymer A is continuously fed through inlet N3 intothe inert gas absorption device N1 by means of transferring pump N2.Then, the prepolymer is continuously fed through perforated plate 4 intothe interior of the inert gas absorption device, into which inert gas Eis introduced through inlet N6 for inert gas. In the inert gasabsorption device, the prepolymer is allowed to fall along and incontact with guides 5. The resultant prepolymer (which contains and/orhas absorbed therein the inert gas) is fed through inlet 2 intopolymerizer 10 by means of transferring pump 7. The prepolymer is thencontinuously fed through perforated plate 4 into the interior(polymerization reaction zone) of polymerizer 10, and is allowed to fallalong and in contact with guides 5.

The pressure in the interior (polymerization reaction zone) ofpolymerizer 10 is controlled so as to maintain a predetermined reducedpressure. The inert gas which is absorbed and/or contained in prepolymerA is released from the prepolymer in the polymerization reaction zone ofthe polymerizer. TMG (which is distilled from the prepolymer) and theinert gas (which is introduced into the polymerizer) are discharged asexhaust gas D through vent 7. The resultant PTT resin B is continuouslywithdrawn from outlet 9 by means of withdrawal pump 8. Inert gasabsorption device N1 and polymerizer 10 are heated by means of a heateror a jacket so as to maintain the temperature inside the polymerizer ata desired level.

In each of the above-mentioned methods, the PTT resin (obtained by apolymerization performed by allowing the prepolymer to fall along and incontact with the guide) which is accumulated at the bottom portion ofthe polymerizer is withdrawn from the outlet by means of a withdrawalpump. It is preferred that the withdrawal of the PTT resin from thepolymerizer is performed in a manner such that the amount of the PTTresin accumulated at the bottom portion of the polymerizer becomes assmall as possible and constant. When the withdrawal of the PTT resin isperformed in such a manner, it becomes easy to prevent the PTT resinfrom suffering disadvantages, such as discoloration (caused by heatdecomposition), lowering of polymerization degree, and fluctuation ofthe quality. The amount of the PTT resin accumulated at the bottomportion of the polymerizer can be controlled by means of transferringpump 1 and withdrawal pump 8, while observing the amount of the PTTresin accumulated at the bottom portion of the polymerizer.

The polymerizer used in the present invention can be equipped with astirrer at the bottom portion thereof, but such a stirrer is notnecessary. Thus, in the method of the present invention, it is possibleto perform a polymerization reaction using a polymerizer having norotary driving part, so that the polymerizer can be tightly sealed evenwhen a polymerization is performed under high vacuum conditions. Thesealability of the rotary driving part of the withdrawal pump isimproved due to the liquid head, as compared to that of a polymerizerhaving a rotary driving part.

The method of the present invention can be conducted using either asingle polymerizer or a plurality of polymerizers. Further, it is alsopossible to use a multi-chamber polymerizer prepared by dividing aninner space of a single polymerizer into a plurality of horizontallyadjacent chambers or a plurality of vertically adjacent chambers.

In the present invention, it is preferred to increase, in advance, thepolymerization degree of the prepolymer (which is to be subjected to theabove-mentioned guide-wetting fall polymerization process) to someextent by at least one polymerization method selected from the followingmethods (a) to (d):

-   -   (a) a polymerization method using a vertical agitation type        polymerizer;    -   (b) a polymerization method using a horizontal agitation type        polymerizer;    -   (c) a polymerization method using a free-fall polymerizer having        a perforated plate; and    -   (d) a polymerization method using a thin film type polymerizer.

Examples of horizontal agitation type polymerizers include a screw-typepolymerizer (such as a single-screw type polymerizer or a twin-screwtype polymerizer) and an independent agitation element type polymerizer,which are described in “Hanno Kougaku Kenkyu-kai kenkyu Repoto:Riakutibupurosessingu Part 2 (Research Group on Reaction Engineering,Research Report: Reactive Processing Part 2)”, Chapter 4, edited by TheSociety of Polymer Science, Japan, 1992.

With respect to the free-fall polymerizer having a perforated plate,reference can be made to, for example, U.S. Pat. No. 5,596,067. When thefree-fall polymerizer is used, a polymerization is performed by allowingthe prepolymer to fall freely from the holes of the perforated plateprovided in the polymerizer. More specifically, a polytrimethyleneterephthalate prepolymer in a molten form is allowed to fall freely fromthe holes of the perforated plate, thereby improving the polymerizationdegree of the prepolymer. Herein, the expression “fall freely” meansthat the prepolymer is allowed to fall without contacting any materials(such as a guide and an inner wall of the polymerizer) which obstructthe fall of the prepolymer. The prepolymer is allowed to fall freely inthe form of a film, a fiber, a droplet, a fog or the like. TMG which isproduced during the polycondensation reaction is withdrawn from thereaction system during the fall of the prepolymer.

In the above-mentioned method using a free-fall polymerizer, there is noparticular limitation with respect to the shape of the holes of theperforated plate, and generally, the shape can be a circle, an ellipse,a triangle, a slit, a polygon, a star or the like. The cross-sectionalarea of each of the holes is generally in the range of from 0.01 to 100cm², preferably from 0.05 to 10 cm², more preferably from 0.1 to 5 cm².Further, the holes can have a nozzle or a short guide attached thereto.However, it is necessary that the nozzle or the short guide is attachedto the holes so that the prepolymer can fall freely after having passedthrough the nozzle or after having fallen along and in contact with theguide. The distance between mutually adjacent holes of the perforatedplate is generally from 1 to 500 mm, preferably from 5 to 100 mm, asmeasured between the respective centers of the mutually adjacent holes.With respect to the distance over which the prepolymer (having passedthrough the holes of the perforated plate) falls freely, the distance ispreferably from 0.3 to 50 m, more preferably from 0.5 to 20 m. Theamount of prepolymer which is caused to pass through the holes variesdepending on the molecular weight of the prepolymer, but is generally inthe range of from 10⁻⁴ to 10⁴ liters/hr, preferably from 10⁻² to 10²liters/hr, more preferably from 0.1 to 50 liters/hr, per hole of theperforated plate. There is no particular limitation with respect to thetime for allowing the prepolymer to fall freely from the perforatedplate, but in general, it is in the range of from 0.01 second to 1 hour.The thus obtained prepolymer may be withdrawn from the polymerizer.Alternatively, the obtained prepolymer may be recycled to the free-fallpolymerizer, and subjected to further free-fall polymerization. Therecycling of the obtained prepolymer to the polymerizer has thefollowing advantage. When the free-fall polymerization is performedwhile recycling the obtained prepolymer, the area of the prepolymersurface renewed per unit time is large, as compared to that in the casewhere the obtained prepolymer is not recycled. Therefore, by recyclingthe obtained polymer to the polymerizer, it becomes easy to achieve adesired degree of polymerization.

Further examples of vertical and horizontal agitation type polymerizersinclude those which are described in “Kagaku Souchi Binran (Handbook ofChemical Apparatuses)”, Chapter 11, edited by The Society of ChemicalEngineers, Japan, 1989. There is no particular limitation with respectto the shape of the vessel, and in general, the shape may be a verticalor horizontal cylinder. Further, there is no particular limitation withrespect to the shape of the agitation element, and the shape ofagitation element can be a paddle, an anchor, a turbine, a screw, aribbon, double wings or the like.

Examples of thin film type polymerizers include a wall-wetting fallpolymerizer, and polymerizers equipped with a centrifugal thin film typeheat exchanger, a liquid film scraping type heat exchanger or the like.As an example of the above-mentioned wall-wetting fall polymerizer,there can be mentioned a polymerizer described in the above-mentioned“Kagaku Souchi Binran (Handbook of Chemical Apparatuses)”, Chapter 11,p. 461, published by The Society of Chemical Engineers, Japan, 1989. Thethin film type polymerizer may have a multi-tubular structure. Further,the prepolymer obtained by the wall-wetting fall may be recycled to thepolymerizer, and subjected to further wall-wetting fall polymerization.Examples of liquid film scraping type heat exchangers and centrifugalthin film type heat exchangers include those which are described in“Netsukoukanki Sekkei Handobukku (Handbook for designing a heatexchanger)”, Chapters 21–22, published by Kougakutosho Ltd., Japan,1974.

The production of a prepolymer from the raw materials can be performedin either a batchwise manner or a continuous manner. When the prepolymeris produced in a batchwise manner, all of the raw materials or the wholeof a reaction product (i.e., a prepolymer having a molecular weightlower than a desired level) are or is charged into a reaction vessel andreacted for a predetermined period of time, and then, the whole of theresultant reaction product is transferred to another reaction vessel. Onthe other hand, when the prepolymer is produced in a continuous manner,raw materials or a reaction product (i.e., a prepolymer having amolecular weight lower than a desired level) are or is continuously fedinto a reaction vessel, while continuously withdrawing the resultantreaction product from the reaction vessel. For obtaining a large amountof a polytrimethylene terephthalate resin having a uniform quality, itis preferred that the production of the prepolymer is performed in acontinuous manner.

With respect to the material of the polymerizer used in the presentinvention, there is no particular limitation. In general, the materialis selected from the group consisting of, for example, stainless steel,nickel and glass lining.

Next, preferred examples of combinations of polymerizers which are usedfor producing a PTT resin from the raw materials are described below,referring to the drawings. However, the combinations of polymerizersusable in the present invention should not be limited to those examples.

FIG. 3 shows an example of a system used for producing the PTT resinfrom terephthalic acid and TMG as raw materials, which system comprisesa combination of vertical agitation type polymerizers and a polymerizerused for performing the guide-wetting fall process. In FIG. 3, mixture Ccontaining raw materials (terephthalic acid and TMG) and a catalyst ischarged into esterification reaction vessel 11, and subjected to anesterification reaction for a predetermined period of time, whilestirring by means of agitation element 12, thereby obtainingbis(3-hydroxylpropyl)-terephthalate (BHPT). The atmosphere inside thereaction vessel is an atmosphere of inert gas, such as nitrogen gas,and/or an atmosphere containing water (steam) and/or TMG which aredistilled from a reaction mixture in the reaction vessel. In general,the pressure inside the reaction vessel is controlled so as to be aroundatmospheric pressure. The water and TMG (which are distilled from thereaction mixture) and/or excess nitrogen gas are discharged from vent 13as exhaust gas D. The BHPT obtained in esterification reaction vessel 11is transferred by means of transferring pump 14 to first verticalagitation type polymerizer 15, where the BHPT is subjected topolymerization for a predetermined period of time, while stirring bymeans of agitation element 16, thereby obtaining a low molecular weightprepolymer A. The inside of the polymerizer is under reduced pressure,or inert gas (such as nitrogen gas) is flowed through the inside of thepolymerizer. The water and TMG (which are distilled from polymer A)and/or excess nitrogen gas is discharged from vent 17 as exhaust gas D.

The low molecular weight prepolymer A obtained in first verticalagitation type polymerizer 15 is transferred by means of transferringpump 18 to second vertical agitation type polymerizer 19, where theprepolymer A is subjected to polymerization for a predetermined periodof time, while stirring by means of agitation element 20, therebyobtaining a prepolymer. The inside of the polymerizer is under reducedpressure, or inert gas (such as nitrogen gas) is flowed through theinside of the polymerizer. The water and TMG (which are distilled fromthe prepolymer A) and/or excess nitrogen gas is discharged from vent 21as exhaust gas D. The prepolymer A having an increased molecular weight,which is obtained in second vertical agitation type polymerizer 19, istransferred and continuously fed through inlet 2 into polymerizer 10 bymeans of transferring pump 1. In polymerizer 10, the prepolymer A iscaused to pass through perforated plate 3, and is introduced into theinterior (polymerization reaction zone) of the polymerizer, where theprepolymer A is allowed to fall along and in contact with guides 5. Thepressure in the polymerization reaction zone is controlled so as to be apredetermined reduced pressure. TMG (distilled from the prepolymer A)and inert gas E (which is optionally introduced into the polymerizerthrough inlet 6 for a gas) if any, are discharged from vent 7. Theobtained PTT resin B is continuously withdrawn from outlet 9 by means ofwithdrawal pump 8.

Esterification reaction vessel 11, first vertical agitation typepolymerizer 15, second vertical agitation type polymerizer 19,polymerizer 10, conduits and transferring pumps are heated by means of aheater or a jacket so as to maintain the temperatures of the reactionvessel, polymerizers, conduits and pumps at desired levels.

FIG. 4 shows an example of a system used for producing the PTT resinfrom terephthalic acid and TMG as raw materials, which system comprisesa combination of a vertical agitation type polymerizer, a horizontalagitation type polymerizer and a polymerizer for performing theguide-wetting fall process. In FIG. 4, mixture C of raw materials(terephthalic acid and TMG) and a catalyst is charged intoesterification reaction vessel 11, and subjected to an esterificationreaction for a predetermined period of time, while stirring by means ofagitation element 12, thereby obtaining BHPT. The atmosphere inside thereaction vessel is an atmosphere of inert gas, such as nitrogen gas,and/or an atmosphere containing water (steam) and/or TMG which aredistilled from a reaction mixture in the reaction vessel. In general,the pressure inside the reaction vessel is controlled to approximatelyatmospheric pressure. The water and TMG (which are distilled from thereaction mixture) and/or excess nitrogen gas are discharged from vent 13as exhaust gas D. The BHPT obtained in esterification reaction vessel 11is transferred by means of transferring pump 14 to first verticalagitation type polymerizer 15, where the BHPT is subjected topolymerization for a predetermined period of time, while stirring bymeans of agitation element 16, thereby obtaining a low molecular weightprepolymer A. The inside of the polymerizer is under reduced pressure,or inert gas (such as nitrogen gas) is flowed through the inside of thepolymerizer. The water and TMG (which are distilled from polymer A)and/or excess nitrogen gas is discharged from vent 17 as exhaust gas D.

The low molecular weight prepolymer A obtained in first verticalagitation type polymerizer 15 is transferred by means of transferringpump 20 to horizontal agitation type polymerizer 22, where theprepolymer A is subjected to polymerization for a predetermined period,while stirring by means of agitation element 23, thereby obtaining aprepolymer A having an increased molecular weight. The inside of thepolymerizer is under reduced pressure, or inert gas (such as nitrogengas) is flowed through the inside of the polymerizer. The water and TMG(which are distilled from polymer A) and/or excess nitrogen gas isdischarged from vent 24 as exhaust gas D. The prepolymer A having anincreased molecular weight, which is obtained in horizontal agitationtype polymerizer 22, is transferred and continuously fed through inlet 2into polymerizer 10 by means of transferring pump 1. In polymerizer 10,the prepolymer A is caused to pass through perforated plate 3, and isintroduced into the interior (polymerization reaction zone) of thepolymerizer, where the prepolymer A is allowed to fall along and incontact with guides 5. The pressure in the polymerization reaction zoneis controlled to a predetermined reduced pressure. TMG (distilled fromthe prepolymer A) and inert gas E (which is optionally introduced intothe polymerizer through inlet 6 for a gas) if any, are discharged fromvent 7. The obtained PTT resin B is continuously withdrawn from outlet 9by means of withdrawal pump 8.

Esterification reaction vessel 11, vertical agitation type polymerizer15, horizontal agitation type polymerizer 22, polymerizer 10, conduitsand transferring pumps are heated by means of a heater or a jacket so asto maintain the temperatures of the reaction vessel, polymerizers,conduits and pumps at desired levels.

Each of FIGS. 5 and 6 shows an example of a system used for producingthe PTT resin from DMT and TMG as raw materials. In each of FIGS. 5 and6, mixture C of raw materials and a catalyst is charged into firsttransesterification reaction vessel 25, and the resultant reactionproduct is transferred to second transesterification reaction vessel 29.In each of first transesterification reaction vessel 25 and secondtransesterification reaction vessel 29, mixture C of raw materials issubjected to a transesterification reaction for a predetermined periodof time, while stirring by means of agitation element (26 or 30),thereby obtaining BHPT. The atmosphere inside the reaction vessel is anatmosphere of inert gas, such as nitrogen gas, and/or an atmospherecontaining methanol and/or TMG which are distilled from a reactionmixture in the reaction vessel. In general, the pressure inside thereaction vessel is controlled to approximately atmospheric pressure. Thevent of each of the reaction vessels is connected to a fractionatingcolumn. TMG distilled from the fractionating column is recycled to thereaction vessel. Methanol and excessive nitrogen are discharged from thefractionating column. The obtained BHPT is subjected to polycondensationin the same manner as mentioned above in connection with the systemsshown in FIGS. 3 and 4, thereby obtaining prepolymer A and then, PTTresin B.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples and Comparative Examples, whichshould not be construed as limiting the scope of the present invention.

In the following Examples and Comparative Examples, various measurementsand analyses were conducted by the following methods.

(1) Intrinsic Viscosity [η]

Intrinsic viscosity [η] of a polymer (i.e., a prepolymer or a finalpolytrimethylene terephthalate resin) was measured by means of an Oswaldviscometer. Specifically, with respect to each of o-chlorophenolsolutions of a polymer, which have different concentrations [C] (g/100ml) of the resin, the relative viscosity [ηsp] was measured at 35° C.The obtained (ηsp/C) values were plotted against the concentrations ofthe resin, and the resultant gradient is extrapolated into the zero (0)concentration to thereby obtain an intrinsic viscosity [η] of thepolymer. That is, the intrinsic viscosity [η] of the polymer wascalculated by the following formula:

$\lbrack\eta\rbrack = {\lim\limits_{Carrow 0}{( {\eta\;{{sp}/C}} ).}}$(2) Crystalline Melting Point

The crystalline melting point of a prepolymer was measured by means of adifferential scanning calorimeter (trade name: Pyris 1; manufactured andsold by Perkin Elmer, Inc., U.S.A.) under the following conditions:

Measuring temperature: 0 to 280° C.

Rate of temperature elevation: 10° C./min

Specifically, a temperature at which an endothermic peak ascribed to themelting of a crystal is observed in the obtained differential scanningcalorimetry (DSC) chart was defined as the crystalline melting point ofthe prepolymer, wherein the determination of the peak was conductedusing an analytic software attached to the calorimeter.

(3) Terminal Carboxyl Group Content

1 g of a polymer (i.e., a prepolymer or a final polytrimethyleneterephthalate resin) was dissolved in 25 ml of benzyl alcohol, followedby addition of 25 ml of chloroform, thereby obtaining a mixture. Theobtained mixture was subjected to a titration with a 1/50 N solution ofpotassium hydroxide in benzyl alcohol. From the obtained titration valueV_(A) (ml) and a blank test value V₀ (ml) which is obtained by atitration conducted in the absence of the polymer, the terminal carboxylgroup content was calculated by the following formula:

Terminal  carboxyl  group  content(meq/kg) = (V_(A) − V₀) × 20.(4) Total Terminal Group Content

The total amount of terminal groups per kg of a sample is defined as thetotal terminal group content. Specifically, the total terminal groupcontent (meq/kg) is calculated from the intrinsic viscosity [η] by thefollowing formula:

Total  terminal  group  content(meq/kg) =   1,000/(polymerization  degree × 206) × 2 × 1,000wherein : the  ploymerization  degree = intrinsic  viscosity[η] × 144.6 − 26.2.(5) Molecular Weight Distribution

The ratio of the weight average molecular weight (Mw) to the numberaverage molecular weight (Mn) (Mw/Mn ratio) was used to evaluate themolecular weight distribution of a polytrimethylene terephthalate resin.The Mw and Mn of a polytrimethylene terephthalate resin were determinedby gel permeation chromatography (GPC). Specifically, the GPC wasconducted under the following conditions:

Apparatus: chromatograph model HLC-8120 (manufactured and sold by TosohCorporation, Japan);

Columns: HFIP804-803 (30 cm) (manufactured and sold by Showa Denko K.K., Japan) (×2);

Carrier: hexafluoroisopropanol;

Measurement temperature: 40° C.; and

Flow rate : 0.5 ml/min.

A calibration curve used in the determination of the Mn and Mw wasobtained by using standard polymethyl methacrylate (PMMA) samples(manufactured and sold by Polymer Laboratories Ltd., U.K.). Themolecular weights of the PMMA samples used were 620, 1,680, 3,805,7,611, 13,934, 24,280, 62,591 and 186,000, respectively.(6) Color (L-value and b*-value)

A pellet of a polytrimethylene terephthalate resin (PTT) was heated at100° C. for 10 minutes to partially crystallize the pellet. The color(in terms of L-value and b*-value thereof) of the obtained partiallycrystallized pellet was measured by means of a color measuring computer(manufactured and sold by SUGA TEST INSTRUMENTS Co., Ltd., Japan).

Separately from the above, another pellet of PTT resin was heated at180° C. for 24 hours, and then, the color thereof was measured in thesame manner as mentioned above, except that the heating at 100° C. forpartially crystallizing the PTT resin was not conducted since the pelletwas already crystallized by the above-mentioned heating at 180° C. Thethus obtained L-value and b*-value of the PTT resin were used as ayardstick of the discoloration of the PTT resin caused by the heating.

(7) Pellet Size

Approximately 2 g of pellets were used as sample pellets. The totalweight of the sample pellets was accurately weighed, and the number ofsample pellets was counted. From the total weight and the number of thesample pellets, the average weight of the pellets was calculated.

(8) Polymer Powder

The amount of polymer powder attached to the surface of pellets wasmeasured as follows.

-   -   1. 1 kg of pellets were placed in a beaker filled with water.    -   2. The pellets in the beaker were stirred for 5 minutes to wash        away the polymer powder from the surface of the pellets.    -   3. The contents of the beaker were filtered through a 30-mesh        filter. Then, the pellets on the filter were repeatedly washed        with water so that broken pieces of pellets and/or polymer        powder would not remain on the pellets.    -   4. The resultant filtrate obtained in step 3 above was filtered        again through a 300-mesh filter. The residue on the filter was        dried at 80° C. under reduced pressure, namely, under a pressure        of 1 kPa. The dried residue was weighed, and the measured weight        was defined as the weight of the polymer powder.        (9) Crystallinity

The density of the pellets was measured in accordance with JIS-L-1013,in which the density of the pellets was measured by gradient densitytube method in which a gradient density tube prepared usingtetrachlorocarbon and n-heptanone was used. The measurement wasconducted with respect to 10 pellets, and the average of the measuredvalues was defined as the density of the pellets. Using the obtainedvalue (ρ_(s)) of the density, the crystallinity of the pellets wascalculated by the following formula:X _(c)(%)={ρ_(c)×(ρ_(s)−ρ_(a))}/{ρ_(s)×(ρ_(c)−ρ_(a))}×100

-   -   wherein ρ_(a) is 1.300 g/cm³ which is an amorphous density of        trimethylene terephthalate homopolymer, ρ_(c) is 1.431 g/cm³        which is a crystal density of trimethylene terephthalate        homopolymer, and ρ_(s) represents a density (g/cm³) of the        pellets.

EXAMPLE 1

Using the device as shown in FIG. 1, production of polytrimethyleneterephthalate resin B was conducted as follows. A polytrimethyleneterephthalate (PTT) prepolymer A having an intrinsic viscosity [η] of0.5 dl/g, a terminal carboxyl group ratio of 7% and a crystallinemelting point of 230° C. was fed through prepolymer feeding inlet 2 intopolymerizer 10 by means of transferring pump 1. In polymerizer 10, PTTprepolymer A was caused to pass through the holes of perforated plate 3in a molten form at 260° C. (temperature of the molten polymer) and at arate of 10 g/min per hole, and then, was allowed to fall along and incontact with guides 5 at an atmospheric temperature of 260° C., which isthe same as the temperature of the molten prepolymer (having passedthrough the holes of perforated plate 3), under reduced pressure,namely, under a pressure of 10 Pa, to thereby perform a polymerizationto obtain PTT resin B. The obtained PTT resin B was withdrawn fromoutlet 9 by means of withdrawal pump 8. The perforated plate had athickness of 50 mm and nine holes, each having a diameter of 1 mm, inwhich the holes of the perforated plate are arranged such that acheckered pattern is formed when lines connecting the holes are drawn onthe surface of the perforated plate. The guide was a wire made ofstainless steel, which wire had a circular cross-section, and had adiameter of 3 mm and a length of 5 m. Guides 5 were attached toperforated plate 4 so that each hole of perforated plate 5 had one guide5 attached thereto. The withdrawal pump was operated while observing thepolymer inside the polymerizer through observing window 4, so thatalmost no polymer was accumulated at the bottom of the polymerizer. (Theabove-mentioned prepolymer A contained titanium tetrabutoxide(polymerization catalyst) and trimethyl phosphate (stabilizer) inamounts of 0.1% by weight and 100 ppm by weight (in terms of the weightof phosphorus), respectively, both of which are based on the weight ofthe prepolymer.) The results are shown in Table 1.

In the above-mentioned polymerization, the retention time was 60minutes. The retention time herein is a value calculated by dividing thetotal amount of the prepolymer and polymer inside the polymerizer by thefeeding rate of the prepolymer.

With respect to the staining of the lower surface of the perforatedplate, which was caused by the foaming of the prepolymer immediatelybelow the holes of the perforated plate, the level of staining was low.

The obtained PTT resin had a high molecular weight, a narrow molecularweight distribution, a low terminal carboxyl group content, andexcellent color. Further, the degree of discoloration of the obtainedPTT resin occurring by heating was very small.

The obtained PTT resin was solidified in cool water having a temperatureof 5° C., and then, cut into pellets, each having a weight of 20 mg. Theamount of polymer powder (which had adhered to the pellets) was as lowas 0.01% by weight, and the pellets had a crystallinity of 5%.Therefore, the obtained pellets were not easily broken and easy tohandle.

EXAMPLES 2 TO 4

In each of Examples 2 to 4, polymerization was performed insubstantially the same manner as in Example 1, except thatpolymerization was performed under the conditions indicated in Table 1.The results are shown in Table 1. In each of Examples 2 to 4, withrespect to the staining of the lower surface of the perforated plate,which was caused by the foaming of the prepolymer immediately below theholes of the perforated plate, the level of staining was low. Theobtained PTT resins had a high molecular weight, a narrow molecularweight distribution, a low terminal carboxyl group content, andexcellent color. Further, with respect to each of the obtained PTTresins, the degree of discoloration occurring by heating was very small.

COMPARATIVE EXAMPLES 1 TO 4

In each of Comparative Examples 1 to 4, polymerization was performed insubstantially the same manner as in Example 1, except that thepolymerization was performed under the conditions indicated in Table 1.The results are shown in Table 1.

In Comparative Example 1, the temperature of the molten preploymerintroduced into the polymerization reaction zone was too high, so that avigorous foaming of the prepolymer occurred just below the holes of theperforated plate, thereby markedly staining the lower surface of theperforated plate. The obtained PTT resin was discolored to assume ayellow color and the color of the PTT resin thereof was non-uniform.Further, the PTT resin suffered severe discoloration by heating.

In Comparative Example 2, the temperature of the molten preploymerintroduced into the polymerization reaction zone was too low, so thatthe prepolymer was solidified, and hence, the prepolymer could not passthrough the holes of the perforated plate.

In Comparative Example 3, the prepolymer had an intrinsic viscosity [η]of 0.18 dl/g, which was too low, so that a vigorous foaming of theprepolymer occurred just below the holes of the perforated plate,thereby markedly staining the lower surface of the perforated plate, andthe inner wall of the polymerizer. The obtained PTT resin contained alarge amount of black impurities (heat deterioration products). Further,the obtained PTT had a low molecular weight.

In Comparative Example 4, polymerization in the polymerizer wasperformed under atmospheric pressure. As a result, it was found that thepolymerization degree of the obtained PTT was not increased, but ratherlowered by the heat decomposition.

EXAMPLE 5

A polymerization was performed in substantially the same manner as inExample 1, except that the guide was changed to a jungle gym-like body,in which wires (each having a diameter of 3 mm) were three-dimensionallyconnected with one another at intervals of 30 mm as viewed in thevertical direction and at intervals of 50 mm as viewed in the horizontaldirection. The upper end portions of the wires extending in the verticaldirection were attached to the holes of the perforated plate. Theresults are shown in Table 1. With respect to the staining of the lowersurface of the perforated plate, which was caused by the foaming of theprepolymer immediately below the holes of the perforated plate, thelevel of staining was low.

The obtained PTT resin had a high molecular weight, a narrow molecularweight distribution, and excellent color. Further, the degree ofdiscoloration of the obtained PTT resin occurred even by heating.

EXAMPLE 6

Polymerization was performed in substantially the same manner as inExample 1, except that the guide was changed to a wire mesh, in whichwires (each having a diameter of 3 mm) were two-dimensionally connectedwith one another at intervals of 30 mm as viewed in the verticaldirection and at intervals of 50 mm as viewed in the horizontaldirection. The upper end portions of the wires extending in the verticaldirection were attached to the holes of the perforated plate. Theresults are shown in Table 1.

With respect to the staining of the lower surface of the perforatedplate, which was caused by the foaming of the prepolymer immediatelybelow the holes of the perforated plate, the level of staining was low.

The obtained PTT resin had a high molecular weight, a narrow molecularweight distribution, a low terminal carboxyl group content, andexcellent color. Further, the degree of discoloration of the obtainedPTT resin occurring by heating was very small.

EXAMPLE 7

Using the production system as shown in FIG. 3, 130 kg of apolytrimethylene terephthalate (PTT) resin was continuously produced perday, in which terephthalic acid and TMG were used as raw materials. Withrespect to the apparatuses used in the above-mentioned productionsystem, each of esterification reaction vessel 11, first verticalagitation type polymerizer 15 and second vertical agitation typepolymerizer 19 was a vertical agitation type polymerizer equipped with astirrer having paddle-shaped agitation blades, and polymerizer 10 wasthe same as used in Example 5.

Specifically, production of the PTT resin was performed as follows.Terephthalic acid and TMG were mixed together (terephthalic acid/TMGmolar ratio=1/1.5), followed by addition of 0.1% by weight of titaniumtetrabutoxide, based on the weight of terephthalic acid, therebyobtaining a mixture (in the form of a slurry). The obtained mixture wascontinuously charged into esterification reaction vessel 11, and apolymerization was performed in substantially the same manner as inExample 1, except that the polymerization was performed under theconditions indicated in Tables 1 and 2, thereby obtaining apolytrimethylene terephthalate (PTT) resin. During the polymerization,trimethyl phosphate (stabilizer) was continuously added to firstvertical agitation type polymerizer 15 in an amount of 20 ppm by weight,based on the weight of the polymer. The results are shown in Table 1.

The prepolymer which was fed into the final polymerizer satisfied therequirements of the present invention, and the obtained PTT resin had ahigh molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

EXAMPLE 8

Using the production system as shown in FIG. 4, 130 kg of apolytrimethylene terephthalate (PTT) resin was continuously produced perday, wherein terephthalic acid and TMG were used as raw materials. Withrespect to the apparatuses used in the above-mentioned productionsystem, each of esterification reaction vessel 11 and first verticalagitation type polymerizer 15 was a vertical agitation type polymerizerequipped with a stirrer having paddle-shaped agitation blades;horizontal agitation type polymerizer 22 was equipped with a uniaxialstirrer having disc-shaped agitation blades; and polymerizer 10 was thesame as used in Example 5.

Specifically, production of the PTT resin was performed as follows.Terephthalic acid and TMG were mixed together (terephthalic acid/TMGmolar ratio=1/1.5), followed by addition of 0.1% by weight of titaniumtetrabutoxide, based on the weight of terephthalic acid, therebyobtaining mixture C (in the form of a slurry). The obtained mixture Cwas continuously charged into esterification reaction vessel 11, andpolymerization was performed in substantially the same manner as inExample 1, except that the polymerization was performed under theconditions indicated in Tables 1 and 3, thereby obtaining apolytrimethylene terephthalate (PTT) resin. During the polymerization,trimethyl phosphate (stabilizer) was continuously added to firstvertical agitation type polymerizer 15 in an amount of 20 ppm by weight,based on the weight of the polymer. The results are shown in Table 1.

The prepolymer which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin had ahigh molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained PTT resin occurring by heatingwas very small.

EXAMPLE 9

Using the production system as shown in FIG. 5, 130 kg ofpolytrimethylene terephthalate (PTT) resin was continuously produced perday, wherein DMT and TMG were used as raw materials. With respect to theapparatuses used in the above-mentioned production system, each of firsttransesterification reaction vessel 25 and second transesterificationreaction vessel 29 was a vertical agitation type polymerizer equippedwith a stirrer having turbine blades (26 or 30); each of first verticalagitation type polymerizer 15 and second vertical agitation typepolymerizer 19 was equipped with a stirrer having paddle-shapedagitation blades (16 or 20); and polymerizer 10 was the same as thepolymerizer used in Example 5, except that the number of holes of theperforated plate was changed to four (wherein the four holes werearranged such that a square is formed when lines connecting the holesare drawn on the surface of the perforated plate); the length of eachguide 5 was changed to 9 m, and the length of the polymerizer casing wasincreased accordingly. During the operation of polymerizer 10, theprepolymer was caused to pass through the holes of the perforated plateat a rate of 23 g/min per hole.

Specifically, production of the PTT resin was performed as follows. DMTand a mixture of TMG and titanium tetrabutoxide (amount of titaniumtetrabutoxide 0.1% by weight, based on the weight of DMT) (DMT/TMG molarratio=1/1.5) were continuously charged into esterification reactionvessel 11, and polymerization was performed under the conditionsindicated in Tables 1 and 4, thereby obtaining a polytrimethyleneterephthalate (PTT) resin. During the polymerization, trimethylphosphate (stabilizer) was continuously added to first verticalagitation type polymerizer 15 in an amount of 20 ppm by weight, based onthe weight of the polymer. The results are shown in Table 1.

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

The obtained polytrimethylene terephthalate resin was immersed in coolwater having a temperature of 5° C. to thereby solidify the PTT resin.The solidified PTT resin was cut into pellets, each having a weight of20 mg. The amount of polymer powder (which had adhered to the pellets)was as low as 0.01% by weight, and the pellets had a crystallinity aslow as 5%. Therefore, the obtained pellets were not easily broken andeasy to handle.

EXAMPLE 10

Polymerization was performed in substantially the same manner as inExample 9, except that nitrogen gas E was introduced through inlet 6into polymerizer 10 in an amount indicated in Table 1, thereby obtaininga polytrimethylene terephthalate (PTT) resin (the conditions employed inthis Example are indicated in Tables 1 and 4). The results are shown inTable 1.

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

EXAMPLE 11

Polymerization was performed in substantially the same manner as inExample 9, except that the production system as shown in FIG. 6 wasemployed instead of the production system as shown in FIG. 5 (i.e.,except that horizontal agitation type polymerizer 22 equipped with auniaxial stirrer having disc-shaped agitation blades 23 was used insteadof second vertical agitation type polymerizer 19), thereby obtaining apolytrimethylene terephthalate resin (the conditions employed in thisExample are indicated in Tables 1 and 5). The results are shown in Table1.

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

EXAMPLE 12

Polymerization was performed in substantially the same manner as inExample 11, except that nitrogen gas E was introduced through inlet 6into polymerizer 10 in an amount indicated in Table 1, thereby obtaininga polytrimethylene terephthalate (PTT) resin (the conditions employed inthis Example are indicated in Tables 1 and 5).

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

EXAMPLES 13 AND 14

In each of Examples 13 and 14, polymerization was performed insubstantially the same manner as in Example 12 (in which the productionsystem as shown in FIG. 6 was employed), except that, in Example 13,guides 5 provided in polymerizer 10 were changed to chains, each formedby the combination of elliptical rings (the diameter of a wire formingeach ring was 3 mm; the major axis of the ellipse defined by each ringwas 50 mm; and the curvature of each ring was 20 mmφ), and that, inExample 14, guides 5 provided in polymerizer 10 were changed to wires,each having a diameter of 5 mm and having welded thereto discs (eachhaving a diameter of 20 mmφ and a thickness of 3 mm) at intervals of 200mm in a manner such that the wire penetrates the center of each disc,thereby obtaining a polytrimethylene terephthalate resin (the conditionsemployed in these Examples are indicated in Tables 1 and 6). The resultsare shown in Table 1.

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

COMPARATIVE EXAMPLE 5

The prepolymer obtained in Example 13 was immersed in cool water havinga temperature of 5° C. to thereby solidify the prepolymer. Thesolidified prepolymer was then cut into pellets, and the pellets weredried at 120° C. in air. 100 kg of the dried pellets were charged into a300 liter tumbling solid-phase polymerizer, and solid-phasepolymerization was performed at 205° C. for 72 hours, while flowingnitrogen gas into the polymerizer at a rate of 100 liters/hr, therebyobtaining a polytrimethylene terephthalate (PTT) resin. The results areshown in Table 1.

The obtained PTT resin had a satisfactorily high molecular weight.However, the obtained resin had a broad molecular weight distribution.Further, the obtained pellets not only had attached thereto polymerpowder in an amount as large as 1.0% by weight, but also had acrystallinity as high as 55%, and hence, the obtained pellet wasbrittle. If it is attempted to transfer the obtained pellets by means ofa feeder or a pneumatic conveyer, the pellets would be broken, therebyforming a large amount of polymer powder.

COMPARATIVE EXAMPLE 6

Polymerization was performed in substantially the same manner as inExample 12, except that the amount of a polytrimethylene terephthalateresin produced per day was reduced to 75 kg, and that polymerizer 10 wasnot used, thereby obtaining a polytrimethylene terephthalate resin. Theresults are shown in Table 1.

The obtained PTT resin had a low polymerization degree, a broadmolecular weight distribution and a high terminal carboxyl groupcontent. Further, the degree of discoloration of the obtained resinoccurring by heating was very large.

EXAMPLE 15

Polymerization was performed in substantially the same manner as inExample 1, except that the system as shown in FIG. 2 was employed inwhich inert gas was introduced into the polymerizer by means of inertgas absorption device N1, and that the polymerization was performedunder the conditions indicated in Table 1. Perforated plate N4 providedin inert gas absorption device N1 had nine holes, each having a diameterof 1 mm, in which the holes of the perforated plate are arranged suchthat a checkered pattern is formed when lines connecting the holes aredrawn on the surface of the perforated plate. Each of guides N5 used ininert gas absorption apparatus N1 was a wire made of stainless steel,which had a circular cross-section, and had a diameter of 5 mm and alength of 3 m. Guides N5 were attached to perforated plate N4 so thateach hole of perforated plate N5 had one guide N5 attached thereto.Nitrogen gas E was fed into the gas absorption apparatus so that theinternal pressure thereof was 0.11 Pa. Prepolymer N5′ was allowed tofall along and in contact with guides N5 so as to cause the prepolymerto absorb and contain nitrogen gas. Transferring pump N7 was operatedwhile observing the prepolymer inside the gas absorption apparatusthrough the observing window, so that almost no prepolymer wasaccumulated at the bottom of the gas absorption apparatus. Prepolymer Awithdrawn from inert gas absorption apparatus N1 contained very smallbubbles. After conducting the production of the PTT resin for a while inthe above-mentioned manner, the feeding of nitrogen gas E into inert gasabsorption apparatus N1 was stopped, and the difference in the internalpressure of inert gas absorption apparatus N1 before and after thestopping of the feeding of nitrogen gas was measured. As a result, itwas found that the difference in the amount of nitrogen gas was 0.5 mgper gram of the prepolymer. This difference in the amount of nitrogengas was defined as the amount of nitrogen gas which was absorbed by andcontained in the prepolymer. Using the thus obtained amount of nitrogengas absorbed by and contained in the prepolymer, the amount of nitrogengas introduced into the polymerizer was calculated on the assumptionthat all nitrogen gas contained in the prepolymer was introduced intothe polymerizer. The results are shown in Table 1. When the prepolymerfalling in polymerizer 10 was observed through observing window 4, itwas found that the prepolymer was in a foaming state and contained alarge amount of bubbles. The resultant polytrimethylene terephthalateresin had a high molecular weight, a narrow molecular weightdistribution and a low terminal carboxyl group content, and excellentcolor. Further, the degree of discoloration of the obtained resinoccurring by heating was very small.

EXAMPLE 16

Polymerization was performed in substantially the same manner as inExample 9, except that the second vertical agitation type polymerizerwas replaced by a free-fall polymerizer (which is the same aspolymerizer 10 of FIG. 5 except that guides 5 were removed so that theprepolymer was caused to fall freely from the holes of perforated plate3), thereby obtaining a polytrimethylene terephthalate resin (theconditions employed in this Example are indicated in Tables 1 and 4).The free-fall polymerizer was operated at 260° C. under a pressure of100 Pa. The results are shown in Table 1.

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

EXAMPLE 17

Polymerization was performed in substantially the same manner as inExample 9, except that the second vertical agitation type polymerizerwas replaced by a thin film type polymerizer (which is the same aspolymerizer 10 of FIG. 5 except that the perforated plate had 4 holesarranged in a line, and that a flat board is vertically provided asguide 5, so that prepolymer A is allowed to fall in the form of a filmon the flat board), thereby obtaining a polytrimethylene terephthalateresin (the conditions employed in this Example are indicated in Tables 1and 4). The thin film type polymerizer was operated at 260° C. under apressure of 100 Pa. The results are shown in Table 1.

Prepolymer A which was fed into the final polymerizer 10 satisfied therequirements of the present invention, and the obtained PTT resin B hada high molecular weight, a narrow molecular weight distribution, a lowterminal carboxyl group content, and excellent color. Further, thedegree of discoloration of the obtained resin occurring by heating wasvery small.

TABLE 1 Property of prepolymer Polymerization Property of polymerDiscol- Intrin- COOH conditions Intrin- COOH oration sic con- Poly- Tem-State of po- sic- con- Non- by viscos- tent COOH mer- per- Pres- N₂lymerization viscos- tent uni- heating ity meq ratio c.m.p. izer aturesure mg/ Foam- Stain- ity Mw meq Color form- Color dl/g /kg % ° C. Guide° C. Pa g ing ing dl/g /Mn /kg b* L* ity b* L* Ex. 1 0.50 15 7 230 Wire260 10 0 ◯ ◯ 1.10 2.3 14 3 90 ◯ 8 88 Ex. 2 0.70 25 19 228 Wire 260 10 0◯ ◯ 1.20 2.3 17 5 91 ◯ 11 89 Ex. 3 0.50 15 7 230 Wire 240 10 0 ◯ ◯ 0.902.2 6 1 87 ◯ 4 87 Ex. 4 0.50 15 7 230 Wire 260 100 0 ◯ ◯ 0.85 2.2 8 3 90◯ 9 90 Ex. 5 0.50 15 7 230 Lat- 260 10 0 ◯ ◯ 1.20 2.3 12 4 92 ◯ 10 90tice Ex. 6 0.50 15 7 230 Wire 260 10 0 ◯ ◯ 1.15 2.3 14 4 92 ◯ 10 91 meshEx. 7 0.40 7 2 228 Wire 260 20 0 ◯ ◯ 1.10 2.3 10 3 90 ◯ 9 89 Ex. 8 0.8020 18 228 Wire 260 20 0 ◯ ◯ 1.20 2.4 14 5 90 ◯ 12 87 Ex. 9 0.45 9 4 230Lat- 250 100 0 ◯ ◯ 1.00 2.3 7 3 90 ◯ 10 89 tice Ex. 0.45 9 4 230 Lat-250 100 4 ◯ ◯ 1.30 2.4 8 7 88 ◯ 11 85 10 tice Ex. 0.60 14 9 230 Lat- 250100 0 ◯ ◯ 1.25 2.3 9 5 88 ◯ 13 82 11 tice Ex. 0.60 14 9 230 Lat- 250 1004 ◯ ◯ 1.40 2.4 14 8 85 ◯ 14 80 12 tice Ex. 0.70 18 14 230 Disc 250 100 0◯ ◯ 1.25 2.3 15 5 88 ◯ 15 80 13 Ex. 0.70 18 14 230 Chain 250 100 0 ◯ ◯1.30 2.3 12 5 88 ◯ 14 80 14 Comp. 0.50 15 7 230 Wire 290 10 0 X X 0.702.6 20 16 88 X 22 81 Ex. 1 Comp. 0.50 15 7 230 Wire 220 10 0 — — — — — —— — — — Ex.2 Comp. 0.18 1 0 232 Wire 260 10 0 X X 0.35 3.2 5 2 93 X — —Ex. 3 Comp. 0.50 15 7 230 Wire 260 At- — ◯ ◯ 0.45 2.2 50 9 86 ◯ — — Ex.4 mos- pher- ic pres- sure Comp. 0.60 14 9 228 Solid- — — — — — 1.30 3.08 2 83 ◯ 18 75 Ex. 5 phase polym- eriza- tion Comp. 0.60 14 9 228 — — —— — — 1.00 2.8 25 8 85 ◯ 27 70 Ex. 6 Ex. 15 0.47 15 7 230 Wire 260 1000.5 100 ◯ 1.30 2.4 6 5 92 ◯ 8 90 Ex. 16 0.40 4 1 230 Lat- 250 100 0 ◯ ◯1.10 2.3 7 3 90 ◯ 9 89 tice Ex. 17 0.60 16 10 230 Lat- 250 100 0 ◯ ◯1.35 2.4 11 8 88 ◯ 15 89 tice Notes: COOH content: Terminal carboxylgroup content (meq/kg). COOH ratio: Terminal carboxyl group ratio (%)(terminal hydroxyl group content/total terminal group content × 100).c.m.p.: Crystalline melting point. N₂: Weight of nitrogen gas per gramof a polymer. Foaming: ◯: Vigorous foaming of the prepolynier was notobserved. X: Vigorous foaming of the prepolyrner was observed. Staining:◯: The lower surface of the perforated plate and/or the inner wall ofthe polymerizer were not stained. X: The lower surface of the perforatedplate and/or the inner wall of the polymerizer were stained.Non-uniformity: ◯: The color of the polymer was uniform. X: The color ofthe polymer was non-uniform. Discoloration by heating: Discoloration asmeasured after heating at 180° C. for 24 hours.

TABLE 2 Tempera- Retention Degree of Intrinsic ture time vacuumviscosity ° C. min. Pa dl/g Esterification 230 200 Atmospheric —reaction pressure vessel First vertical 250 60 40000  0.2 agitation typepolymerizer Second vertical 255 60 2000 See Table 1 agitation typepolymerizer Notes: Intrinsic viscosity: The intrinsic viscosity of theproducts dis-charged from each of the reaction vessel and thepolymerizers.

TABLE 3 Tempera- Retention Degree of Intrinsic ture time vacuumviscosity ° C. min. Pa dl/g Esterification 230 200 Atmospheric —reaction pressure vessel First vertical 250 60 20000  0.3 agitation typepolymerizer Horizontal 255 60 700 See Table 1 agitation type polymerizerNotes: Intrinsic viscosity: The intrinsic viscosity of the productsdis-charged from each of the reaction vessel and the polymerizers.

TABLE 4 Tempera- Retention Degree of Intrinsic ture time vacuumviscosity ° C. min. Pa dl/g First 190 120 Atmospheric — transesterifi-pressure cation reaction Vessel Second 220 120 Atmospheric —transesterifi- pressure cation reaction vessel First vertical 255 601000  0.3 agitation type polymerizer Second vertical 260 60 100 SeeTable 1 agitation type Polymerizer Notes: Intrinsic viscosity: Theintrinsic viscosity of the products dis-charged from each of thereaction vessels and the polymerizers.

TABLE 5 Tempera- Retention Degree of Intrinsic ture time vacuumviscosity ° C. min. Pa dl/g First 190 120 Atmospheric — transesterifi-pressure cation reaction vessel Second 220 120 Atmospheric —transesterifi- pressure cation reaction vessel First poly- 255 60 1000 0.3 condensation reaction vessel Horizontal 260 60 100 See Table 1agitation type polymerizer Notes: Intrinsic viscosity: The intrinsicviscosity of the products dis-charged from each of the reaction vesselsand the polymerizer.

TABLE 6 Tempera- Retention Degree of Intrinsic ture time vacuumviscosity ° C. min. Pa dl/g First 190 120 Atmospheric — transesterifi-pressure cation reaction vessel Second 220 120 Atmospheric —transesterifi- pressure cation reaction vessel First poly 255 60 500 0.35 -condensation reaction vessel Horizontal 260 60 50 See Table 1agitation type polymerizer Notes: Intrinsic viscosity: The intrinsicviscosity of the products dis-charged from each of the reaction vesselsand the polymerizer.

TABLE 7 Tempera- Retention Degree of Intrinsic ture time vacuumviscosity ° C. min. Pa dl/g First 180 180 Atmospheric — transesterifi-pressure cation reaction vessel Second 210 180 Atmospheric —transesterifi- pressure cation reaction vessel First poly 255 120 500 0.55 -condensation reaction vessel Horizontal 260 120 50 See Table 1agitation type polymerizer Notes: Intrinsic viscosity: the intrinsicviscosity of the products dis-charged from each of the reaction vesselsand the polynierizer.

INDUSTRIAL APPLICABILITY

The polytrimethylene terephthalate resin of the present invention can bestably produced on a commercial scale without performing solid-phasepolymerization. Further, the polytrimethylene terephthalate resin of thepresent invention has an intrinsic viscosity within an appropriaterange, a narrow molecular weight distribution, and excellent color, andhence, can advantageously be used for stably producing a fiber or shapedarticle which has high strength and excellent color on a commercialscale.

1. A polytrimethylene terephthalate resin comprising: 90 to 100 mole %of trimethylene terephthalate recurring units, and 0 to 10 mole % of atleast one monomer unit selected from the group consisting of monomerunits obtained from comonomers which are other than the monomers usedfor forming said trimethylene terephthalate recurring units and whichare copolymerizable with at least one of the monomers used for formingsaid trimethylene terephthalate recurring units, said polytrimethyleneterephthalate resin having the following characteristics (A) to (D): (A)an intrinsic viscosity [η] of from 0.8 to 4.0 dl/g; (B) a molecularweight distribution of from 2.0 to 2.7 in terms of the Mw/Mn ratio,wherein Mw represents the weight average molecular weight of saidpolytrimethylene terephthalate resin and Mn represents the numberaverage molecular weight of said polytrimethylene terephthalate resin;(C) a psychometric lightness L-value (L-1) of from 70 to 100 and apsychometric chroma b*-value (b*-1) of from −5 to 25; and (D) apsychometric lightness L-value (L-2) of from 70 to 100 and apsychometric chroma b*-value (b*-2) of from −5 to 25 as measured afterheating said polytrimethylene terephthalate resin at 180° C. for 24hours in air.
 2. The polytrimethylene terephthalate resin according toclaim 1, wherein said polytrimethylene terephthalate resin has anintrinsic viscosity [η] of from 1.25 to 2.5 dl/g.
 3. Thepolytrimethylene terephthalate resin according to claim 1, which has aterminal carboxyl group content of from 0 to 20 meq/kg.
 4. Thepolytrimethylene terephthalate resin according to claim 1, which has amolecular weight distribution of from 2.0 to 2.6.
 5. Thepolytrimethylene terephthalate resin of any one of claims 1 to 4, whichis in the form of pellets.
 6. The polytrimethylene terephthalate resinaccording to claim 5, wherein said pellets have an average weight offrom 1 to 1000 mg per pellet, and wherein said pellets contains a powderof said polytrimethylene terephthalate resin in an amount of 0 to 0.5%by weight, based on the total weight of said pellets, which powderpasses through a 30-mesh filter and does not pass through a 300-meshfilter.
 7. The polytrimethylene terephthalate resin according to claim5, wherein said pellets have a crystallinity (X_(c)) of 40% or less,wherein said crystallinity is defined by the following formula:X _(c)(%)={ρ_(c)×(ρ_(s)−ρ_(a))}/{ρ_(a)×(ρ_(c)−ρ_(a))}×100 wherein ρ_(a)is 1.300 g/cm³ which is an amorphous density of trimethyleneterephthalate homopolymer, ρ_(c) is 1.431 g/cm³ which is a crystaldensity of trimethylene terephthalate homopolymer, and ρ_(s) representsa density (g/cm³) of said pellets.
 8. A method for producing apolytrimethylene terephthalate resin, which comprises: (1) providing amolten form of a trimethylene terephthalate prepolymer comprising: 90 to100 mole % of trimethylene terephthalate recurring units, and 0 to 10mole % of at least one monomer unit selected from the group consistingof monomer units obtained from comonomers which are other than themonomers used for forming said trimethylene terephthalate recurringunits and which are copolymerizable with at least one of the monomersused for forming said trimethylene terephthalate recurring units, saidtrimethylene terephthalate prepolymer having an intrinsic viscosity [η]of from 0.2 to 2 dl/g, and (2) polymerizing said molten form of atrimethylene terephthalate prepolymer at a temperature which is 5° C. ormore higher than the crystalline melting point of said prepolymer but isnot higher than 280° C. under reduced pressure by the guide-wetting fallprocess in which said prepolymer is allowed to fall along and in contactwith the surface of a guide so that polymerization of said prepolymer iseffected during the fall thereof.
 9. The method according to claim 8,wherein said molten prepolymer is continuously fed to a polymerizationreaction zone for effecting the polymerization of said prepolymer insaid step (2) and the resultant polytrimethylene terephthalate resinproduced in said step (2) is continuously withdrawn from saidpolymerization zone, so that said step (2) for prepolymer polymerizationis continuously performed.
 10. The method according to claim 8, whereinsaid guide has at least one portion selected from the group consistingof a concave portion, a convex portion and a perforated portion.
 11. Themethod according to claim 8, wherein said prepolymer falling along andin contact with the surface of said guide is in a foaming state.
 12. Themethod according to claim 8, wherein the polymerization in said step (2)is performed, while introducing inert gas to said polymerizationreaction zone.
 13. The method according to claim 12, wherein the amountof said inert gas introduced to said polymerization reaction zone is inthe range of from 00.5 to 100 mg per gram of said polytrimethyleneterephthalate resin withdrawn from said polymerization reaction zone.14. The method according to claim 12, wherein at least a part of saidinert gas is introduced to said polymerization reaction zone in a mannerwherein the introduction of the part of said gas is conducted separatelyfrom the feeding of the trimethylene terephthalate prepolymer to thepolymerization reaction zone.
 15. The method according to claim 12,wherein at least a part of said inert gas is introduced to saidpolymerization reaction zone in such a form as absorbed or contained insaid trimethylene terephthalate prepolymer.
 16. The method according toclaim 8, wherein said prepolymer has an intrinsic viscosity [η] of from0.5 to 2.0 dl/g and a terminal carboxyl group ratio of 50% or less interms of the molar ratio (%) of the terminal carboxyl groups of theprepolymer to all terminal groups of the prepolymer.
 17. The methodaccording to claim 8, wherein said prepolymer is produced by at leastone polymerization method selected from the following methods (a) to(d): (a) a polymerization method using a vertical agitation typepolymerizer; (b) a polymerization method using a horizontal agitationtype polymerizer; (c) a polymerization method using a free-fallpolymerizer having a perforated plate; and (d) a polymerization methodusing a thin film type polymerizer.
 18. The method according to claim17, wherein said prepolymer is produced by said method (b).
 19. Apolytrimethylene terephthalate resin produced by the method of any oneof claims 8 to
 18. 20. A polytrimethylene terephthalate resin producedby a process comprising: providing a molten form of a trimethyleneterephthalate prepolymer comprising: 90 to 100 mole % of trimethyleneterephthalate recurring units, and 0 to 10 mole % of at least onemonomer unit selected from the group consisting of monomer unitsobtained from comonomers which are other then the monomers used forforming said trimethylene terephthalate recurring units and which arecopolyrnerizable with at least one of the monomers used for forming saidtrimethylene terephthalate recurring units; and polymerizing sold moltenform of a trirnethylene terephihalate prepolymer by the guide-wettingfall process in which said prepolymer is allowed to fall along and incontact With the surface of a guide so that polymerization of saidprepolymer is effected during the fall thereof, wherein thepolytrimethylene terephthalate resin has a molecular weight distributionof from 2.0 to 2.7 in terms of the Mw/Mn ratio, wherein Mw representsthe weight average molecular weight of said polytrimethyleneterephthalate resin and Mn represents the number average molecularweight of said polytrimethylene terephthalate resin.